Achievements - labri.fr - C… · ACHIEVEMENTS. 2.1. COMBINATORICS AND ALGORITHMS 25...

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Achievements

22 CHAPTER 2. ACHIEVEMENTS

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Before presenting in detail the scientific achievements of the teams of LaBRI, we rapidly give someelements which interest the LaBRI community at large.

Continuing the work of the previous directors, we have strived to reinforce the lab’s capacity to be aconstructive actor of the development of our discipline locally, nationally and internationally. This goesthrough a continued support to the lab members’ projects, and especially to emerging projects; through adetermined presence in the campus-wide and regional initiatives, to assert the importance of informationsciences in all fields of science and industry, and to be able to participate in IdeX-, University- or Region-supported programs; and through the evolution of the lab’s services to better support the logistics of ourscientific projects.

In this spirit, we have for instance established clear procedures that allow the lab members to receivehigh-level advice when designing the budgetary dimension of their projects (Region, ANR, industry), butalso, on a very day-to-day level, to facilitate the organization of their travels, of their invitations and of thework of their interns. This was achieved through a continuous evolution of the administrative services, thecreation of new functions such as assistantes d’équipes, etc.1.

In addition, we have invested more efforts in our communication strategy, entrusted to a team composedof an administrative staff and a faculty member. As indicated in a previous section, we have also heavilyinvested in the strengthening of our industrial relations and technology transfer service (RITT) and in thedevelopement of shared computational and hardware platforms.

1It must be added that our work was not made easier by the rapid changes of our institutional environment and by theinsufficient number of permanent administrative staff. We also observed a remarkable increase of the level of bureaucraticcomplexity, paradoxically accompanying efforts to simplify the machinery. For instance, the smart dematerialization of billsand invoices and the creation of a service facturier at CNRS and at Université de Bordeaux, leads to an increase of thenumber and complexity of documents to be stored (and materialized!) on site. The regulation on public markets forces us towork, among others, with travel agencies that are poorly efficient, and that require increased work on the part of the LaBRIadministrative staff if we are to obtain decently priced services. The welcome budgetary autonomy of the labs now enforcedby CNRS, with the loosening of the separation between different budget lines, is accompanied by a growing monitoring of ourbudgetary execution and intense pressure to meet trimestrial expenditure objectives. . .

2.1. COMBINATORICS AND ALGORITHMS 25

2.1 Combinatorics and Algorithms

2.1.1 Members

PR MCF DR CR TotalJanuary 1, 2009 9 13 3 7 32June 30, 2014 10 14 7 5 36

PhDs defended2: 25On-going PhDs1: 16Post-doctoral fellowships: 192 months

Staff (on 2014/06/30): ALEXANDRE Frédéric (DR), AVAL Jean-Christophe (CR HDR), BAUDONOlivier (MCF), BEAUMONT Olivier (DR), BIANCHI Giuliana (MCF), BONICHON Nicolas (MCF HDR),BOUSQUET-MÉLOU Mireille (DR), BOUSSICAULT Adrien (MCF, Deputy Team Leader), CORIRobert (PR emeritus), DELECROIX Vincent (CR), DELMAS Olivier (MCF), DORBEC Paul (MCF HDR),DUCHON Philippe (PR), EYRAUD-DUBOIS Lionel (CR), GAVOILLE Cyril (PR), GUIBERT Olivier(MCF), HANUSSE Nicolas (DR, Theme leader Distributed Algorithms), HOCQUARD Hervé (MCF),ILCINKAS David (CR), JOHNEN Colette (PR), KARDOS Frantisek (MCF), KLASING Ralf (DR, Teamleader), MARCKERT Jean-Francois (DR, Theme leader Enumerative and Algebraic Combina-torics), MAZOIT Frédéric (MCF), METIVIER Yves (PR), MILANI Alessia (MCF), NARBEL Philippe(MCF), PECHER Arnaud (PR, Theme leader Graphs and Applications), RASPAUD André (PRemeritus), ROBSON Mike (PR emeritus), ROUGIER Nicolas (CR HDR), SOPENA Eric (PR), TRAVERSCorentin (MCF), VIENNOT Xavier (DR emeritus), ZEMMARI Akka (MCF HDR), ZVONKINE Alexandre(PR)

Hired Postdocs (2009/01/01-2014/06/30)3: BAMPAS Evangelos (2009-2010, 2014-2015), BEAUDOULaurent (2010), BULTEL Jean-Paul (2011-2012), CHAN Yao-ban (2011-2012), GUERRINI Eleonora (2010),KIM Yusik (2009-2011), KOSOWSKI Adrian (2008-2009), KOVSE Matjaz (2010-2012), LABOUREL Ar-naud (2009-2010), LORENZO Juan Angel (2013-2014), NASERASR Reza (2010-2011), RENAUD-GOUDPaul (2012-2013), SILIMBANI Matteo (2012-2013), THRAVES-CARO Christopher (2008-2009), WONYoung (2010-2011)

PhD students (on 2014/06/30): BARJON Matthieu, BONNIN David, BOUVIER Tom, CAPDE-VIELLE Claire, CARRERE Maxime, CASSE Jérôme, COURTIEL Julien, DUFFY Christopher, DUVI-GNAU Romaric, GILLET Noël, HALFTERMEYER Pierre, KAMNANG WANKO Patrick, KUMAR Suraj,NEGGAZ Mohamed Yessin, OULED ABDALLAH Nesrin, SELIG Thomas, TOPALIDOU Meropi, TOUTOmar

2.1.2 Scientific reportDiscrete structures appear in all sciences: biology, mathematics, physics, and of course computer science,where they play a special role since computers work with discrete objects only. Thus, the file system in acomputer, a data structure, the encoding of a DNA strand, a computer network, are combinatorial objects:trees, tables, words, graphs. Mainly motivated by computer science issues and applications, the Combina-torics and Algorithms team seeks to understand, to describe, and sometimes to define these structures. Italso contributes to designing, analyzing and optimizing the algorithms working on these objects.

Three main interrelated directions of research are followed by the team, and they correspond to its divisioninto themes (Distributed algorithms, Enumerative and algebraic combinatorics, Graphs and applications),whose areas of interests are developed below. Here are already some keywords: enumeration/decompositionof structures, determination of their properties, either intrinsic (for instance properties of colourability ingraph theory) or statistical (the study of the distribution of some parameters in a class of random objects),

2PhDs co-supervised by two teams are counted as 0.5.3The list comprises all postdocs and all external temporary assistant professors (ATER).


random generation, graph colouring, ... This knowledge in turn leads to the design of more efficient algorithmsand the study of their complexity, particularly in the domain of distributed and/or probabilistic algorithms,and the research for compact data structures and encodings which allow efficient computations.

The three research themes have roughly the same size. Each of the research themes is very active andbenefits from its own international visibility, but the themes are not independent at all. On the contrary,about a quarter of the team members take part in several themes. Numerous joint publications between thethemes show that the interaction between themes is a reality. Overall, this leads to an excellent cohesionand synergy of the team. Moreover, the team is marked by a high degree of dynamism. This is for examplewitnessed by the fact that each research theme organizes its own working group on a weekly basis. In addition,the team has started a transversal working group on “Probability and Computer Science” which has had anenormous success inside and outside the team. The team is also regularly involved in the organisation ofnational and international conferences.

The three research themes are intermingled with three INRIA project teams: Cepage, Realopt andMnemosyne. The positioning of these three INRIA teams is as follows. First, the Cepage project whichfinished at the end of 2013, was devoted to the design of algorithms and data structures for large scaledynamic platforms. All of its 10 permanent members (INRIA+CNRS+University) were affiliated to theLaBRI and members of our team. Realopt aims at solving practical combinatorial optimization applications.It comprises predominantly members of the IMB (Bordeaux Mathematics Institute) and three members ofour team participate now. The case of the Mnemosyne project (working on the design of distributed modelsof the brain) is a bit different since it involves members of the IMN (Institute for Neurodegenerative Dis-eases), two of its permanent members (including the project leader) being affiliated to the LaBRI. This teamhas been integrated into the Combinatorics and Algorithms team after its arrival from Nancy, two years ago,on a temporary basis. This attachment is currently being reviewed.

We would like to emphasize what we consider the strengths of the Combinatorics and Algorithms team:first its high level of publications; a solid international reputation (shown notably by our involvement inconference organisations, journal editing and many collaborations including funded projects); the strongcoherence and the high dynamism of the team and the themes; our ability to give rise to new researchprojects (e.g. development of probabilistic aspects, links with statistical physics); our ability to cope withthe high fluctuation in the members of the team (due to retirements and new recruitments); the high numberof Ph.D./HDR theses defended in the team (9 HDRs + 26 PhDs); the distinctions of our team members(e.g. 1 junior member IUF, 1 silver medal CNRS, 1 laureate of the Peccot Foundation, Collège de France);our ability to recruit excellent candidates as MCF or CNRS / INRIA researchers; and finally the excellenceof our team members which has led to several promotions (e.g. 3 promotions from CR1 to DR2 level) and tosome of them being recruited in other academic institutions (inside and outside of France) as Full Professorsor Assistant/Associate Professors.

We will now give a synthetic presentation of selected results obtained by our team in the period ofreference. The presentation starts with the three research themes, followed by the three INRIA project-teams.Distributed Algorithms. About 15 permanent researchers are involved in the “Distributed Algorithms”group. Members meet in an open and weekly seminar attracting at least 30 participants (including also non-permanent researchers and researchers from the teams “Formal Methods” and “Programming, Networks andSystems”). Among the 15 members, 8 of them also belong to the INRIA project-team Cepage (until 2013),2 of them to the INRIA project-team Mnemosyne and 2 to the transversal project VISIDIA.

In our group, we focus on the study of formal models and on the design of reliable distributed algorithmsfor large-scale networks. Networks size keeps on increasing, and providing reliable communication is still achallenging task. The majority of our results consists of either impossibility results or the design of algorithmswith provable performance guarantees, in several settings. Our team has a recognized world-wide expertiseattested by numerous publications in the best conferences and journals (more than 100 international papersin 5 years): STOC, SODA, PODC, DISC, IPDPS, ICALP, STACS, Distributed Computing, Information andComputation, Algorithmica, Journal of Parallel and Distributed Computing, etc. Although our group is con-stituted of theoretical researchers, we also participate in industrial projects: SIMID (Aeronautics), STREP7 European project “EULER” (Routing, with Alcatel-Lucent Bell), Investissement d’Avenir SPEEDDATA(Distributed Data Mining Computing, with AT-Internet).

The main scientific topics investigated by our group are the following:


• Distributed computational models, expressivity and formal proofs of distributed algorithms. We aim atproviding models and tools in order to take into account all the aspects of distributed computing. Ourmethod consists in supplying rigorous proofs using either a formal proof management system like Coq(for semi-interactive development of machine-checked proofs) or convenient computational models. Forinstance, the local computation model has been proposed by LaBRI members and many results havebeen proved in this framework, like the expressivity of the Hoare model, for which the exchange betweentwo neighbouring nodes is synchronous [RI80], graph characterizations for the election problem [RI79].In [RI150], the notion of distributed checkability is proposed in the context of wait-free, shared memorysystems.

• Reliable and self-stabilizing distributed computing. A distributed system can suffer from frequent dys-functions due to permanent/temporary failures or crashes, and/or to the dynamicity of the network.We focus on different tasks like consensus, agreement, election, failure detection, cluster maintenance,enforcing several properties like wait-freedom, obstruction-freedom, self-stabilization, etc. For instance,a universal construction provides a general mechanism for obtaining a concurrent implementation ofany object from its sequential code. Disjoint-access parallelism guarantees that processes operatingon different parts of an implemented object do not interfere with each other. This permits increasedparallelism. Wait-freedom guarantees progress for each non-faulty process, even when other processesrun at arbitrary speeds or crash. We prove that no universal construction can ensure both properties[CI108]. In [RI179], a self-stabilizing algorithm builds clusters of bounded diameter, minimizing thenumber of clusters and providing a minimal service before reaching a legal configuration.

• Large-scale networks modeling and resource allocation. Many synthetic or real networks share topologicproperties (heterogeneity of bandwidth, small-world phenomenon, heterogeneous degree distribution,etc). Taking into account these properties is very important for the efficiency of algorithms. We tacklesome problems like resource allocation and scheduling [CI39], broadcast [RI40], light routing tablesmaintenance [CI124], etc. We also work on proposing new relevant models. By relevant, we mean thatthe parameters can be set easily and lead to polynomial-time algorithms for classical problems.

• Massive distributed data and compact data structures. How to maintain and design light data struc-tures in order to answer quickly many requests? We deal with distributed hash tables, compactrouting schemes (the maintenance of compact routing data structures avoiding the traversal of pat-terns of nodes/edges, compact routing schemes [CI2], ...), geometric/non geometric spanning subgraphs(spanners, Delaunay) [CI54] and more recently data mining requests (frequent items, functional depen-dencies, ...) [CI36]. All of our results are economical in terms of memory, and/or fast and competitivewith respect to centralized algorithms.

• Probabilistic distributed algorithms. Impossibility results or poor performance of some deterministicdistributed algorithms are well-known. We worked on randomized algorithms whose performance isexpressed in terms of bit or message complexity: we derived optimal time and bit complexity for theminimal independent set (messages of size one bit, O(logn) rounds) [RI219], coloring and maximalmatching for anonymous graphs without any knowledge on parameters (size, diameter) of the network[RI47], a new distributed election algorithm with any provided precision [CI177].

Among these different fields of research, we may also underline that some of them are recent (startedafter 2009) and quite original: many contributions on mobile agent computing (perpetual exploration byteams [CI163, CI94], resource finding [CI137], etc.), the design of transactional memory algorithms and ofself-stabilizing algorithms, and distributed data mining.

Enumerative and algebraic combinatorics. About 12 permanent researchers are involved in the “Enu-merative and Algebraic Combinatorics”(CEA) group.

The main activity of the group consists in obtaining results of a mathematical nature describing discreteobjects and their properties. Most of these objects play a central place in computer science and our techniquesalso apply to the analysis of algorithms and to the study of statistical physics models, among others. Themain objects studied by CEA are trees, paths, permutations, tableaux, combinatorial maps, polynomials,words.


The first step in the study of a family of discrete objects is always to understand their structure: canthey be encoded in a simple fashion, decomposed recursively? Can they be produced (exhaustively or atrandom) by a simple algorithm? Are they in bijection with some better known objects? A first objectiveis to count objects of size n, but one also studies additional parameters as, for example, the diameterof a graph of size n. The enumeration with respect to several parameters combined with an asymptoticstudy of the results provides quantitative information on the general shape of the objects: for instance,the mean height of a planar tree with n vertices has order n1/2. In the most favourable cases, one obtainslimiting probability distributions for parameters. Using probabilistic tools, it is sometimes possible to showthat suitably normalised large combinatorial objects can be well approximated by some continuous randomobjects. We often support such limit results by simulations of large random objects.

Certain families of discrete objects possess in addition an algebraic structure – group, ring, algebra– which can be studied per se. A famous example is the set of permutations on n letters which forms agroup whose theory of representations by Young tableaux and polynomial incarnation (the ring of symmetricpolynomials) gives rise to a rich and flourishing area of combinatorics.

The CEA group already has a long history, and is one of the leaders in its domain with a very goodinternational visibility. The group is involved in many events and structures, like the LIA LIRCO (CNRSinternational research group), important conferences (FPSAC), editorial boards (JCTA), or invited lectures.At the national level, CEA helps to federate and organise the community, inside the GT ALEA of the GDRIM. It has founded and organised these past 5 years a major national event in combinatorics: the “Journéesde combinatoire de Bordeaux”, a conference where the speakers are invited from all parts and groups ofFrance, and a large space is given to PhD students and young researchers.

Let us now be a bit more specific on some contributions of the group. The study of permutations isat the heart of the ANR project PSYCO. Among other things, the introduction of new objects, called“tree-like tableaux”, has turned out to be a powerful tool to unify many existing bijections between labelledtrees and permutations [RI18, RI17]. Other contributions concern co-invariants of the symmetric group[RI15, RI20]. Algebraic combinatorics related publications include [CI21, RI201, RI155, RI158] and [ON2](dessins d’enfants and maps).

In statistical physics, one finds numerous discrete models that aim at describing the macroscopic be-haviour of a large collection of microscopic elements, based on their (microscopic) interactions. The solutionof numerous such models boils down to an enumerative problem. Our contributions in this field deal forinstance with lattice animals [RI203, RI24], self-avoiding walks [RI37, RI25], sand-pile model [RI208, AI57],or the Potts model on random planar maps [RI46, II5].

Other studies of the group concern almost all aspects of enumerative combinatorics: permutations [RI67,RI94, RI93], fully packed loops [RI21], maps [RI47, RI46, RI91], walks in the quarter plane [RI58], geometricalgraphs [RI204], words [CI92], convergence in distribution to random continuous limits [RI74, RI206], etc.

Graphs and applications. About 20 permanent researchers are involved in the “Graphs and applications”group. Among the 20 members, 3 of them also belong to the INRIA project-team Realopt.

Graph theory constitutes a powerful tool for modelling and understanding complex combinatorial struc-tures. The researches of this thematic group focus on the development of this theory with a special concernfor its applications, specifically in the field of communications in networks. Many problems we study arecoming from recent developments of classical problems, either as a tool for understanding better the initialproblem (e.g. oriented colourings, which were introduced and developed at the LaBRI before becoming awidely studied topic in the international community), or as a way to address specific applications (e.g. graphpartitioning for resource sharing or power domination for electrical network monitoring).

Members of the group have set up many projects, including the ANR projects ALADDIN, DORSO,GraTel, IDEA, and participate in many other projects. We have also established strong international part-nerships with many countries, such as United Kingdom, China, Israel, Poland, Czech Republic, Slovakia,Taiwan, South Africa, Slovenia, etc.

The team covers a wide range of graph theory topics (the exhibited references constitute a selection ofthe major ones):

• Graph colourings and graph homomorphisms historically constitute the core of the group topics. It wasalso the topic of the GraTel project. The group is often initiating research work on this topic that arethen widely studied by the international community. The main topics in this area include chromatic

http://www.labri.fr/perso/aval/LIRCO/lirco.html


number [RI72], list chromatic number [RI89], adaptable chromatic number [RI213], oriented chromaticnumber [RI244], strong edge coloring [RI172].

• During the last five years, many new topics started in the team, motivated by applications. Identifyingcodes were studied especially within the ANR project IDEA [RI110]. Resource sharing gave rise tonew research work on graph partitioning, in particular with the Ph.D. work of J. Bensmail [RI28]. Tohandle electrical networks monitoring problems, studies of power domination and other dominationrelated questions were initiated [RI83]. Fullerenes and their properties are studied for chemical appli-cations [CHI10]. Other recently started problems include in particular signed graphs [RI221], but alsoorthogonal packing problems and appropriate graph algorithms [RI182], and finally, a bit further fromclassical graph theory, combinatorial game theory, with (among others) the Ph.D. work of G. Renault[RI222].

• Other topics are motivated by cooperation with other groups, such as routing [CI54] in collaborationwith the distributed algorithms group, and mathematical programming [RI227] in particular in thecontext of the INRIA project-team Realopt.

EPI Cepage. The INRIA project-team Cepage was launched when the development of interconnectionnetworks had led to the emergence of new types of computing platforms, characterized by the heterogeneity ofboth their processing and communication resources, their geographical dispersion, the absence of centralizedcontrol, and their instability in terms of the number and performance of participating resources. In thiscontext, the general goal of Cepage was to come up with new strategies in order to extend the set ofcomputation-intensive applications that could be run on large scale distributed platforms. This was achievedby gathering researchers with expertise in scheduling of tasks and collective communications, graph theory,design of overlay networks, modeling of network topologies, small world networks, distributed algorithms,compact data structures, routing and randomized algorithms, later extended to include mobile agents anddatabases.

Our work is organized into three main axes:

• Resource Allocation and Scheduling, with an emphasis on the interaction between network performancemodeling and the design of efficient and guaranteed algorithm: our main originality is to consider thewhole chain (models + algorithms + implementation), from gathering actual data on the network toplatform modeling and complexity analysis;

• Compact Routing, with an emphasis on the design of specific strategies for restricted graph classes andthe design of data structures resilient to resource failures: we managed to obtain sub-linear size routingtables (in the number of nodes of the platform) while guaranteeing almost shortest paths (stretch 1 + εor 3 for arbitrary topology);

• Mobile Agents, with an emphasis on the detection of dynamic faults and improvement of dissemi-nation of information (exploring, monitoring, ...). The work of Cepage has focused on contributingnew decentralized algorithms for controlling mobile entities known as agents, deployed in unknownenvironments.

EPI Realopt. The Realopt research agenda is to develop theory, methodologies and algorithms with theaim of solving practical combinatorial optimization applications, extending the scale of input data thatcan be dealt with, and/or integrating more decision levels into its models. In the last 5 years, the mainachievements at the core of the project included:

• a column-and-row generation approach bridging the gap with polyhedral and extended formulationapproaches;

• progress in developing further column generation algorithms;

• polyhedral work in linear and non-linear mixed integer programming.


With the help of the “Graph and Applications” theme, polyhedral characterizations of combinatorialproblems in a variety of graphs have also led to significant progress on the algorithmic side: for instancewith the tremendous progress made on solving the maximum weighted stable set problem in a claw-freegraph (with complexity n3 versus n6, where n is the number of vertices). A lot of progress on stabilityand chromatic numbers has been accomplished, generalizing the concepts to circular-chromatic number andstudying special classes of graphs such as planar graphs or a-perfect graphs with strong algorithmic results.In terms of applications, new efficient algorithms for the orthogonal knapsack problem have been developedand also for the reliable service allocation problem in clouds with memory and capacity constraints.

The team has published in highly regarded journals such as Mathematical Programming, Discrete Math-ematics, Combinatorica, Journal of Graph Theory, Discrete Optimization, European Journal of Combina-torics, and selective conferences such as ACM-SIAM Symposium on Discrete Algorithms (SODA).

EPI Mnemosyne. Our group joined the “Combinatorics and Algorithms” team in 2012. Although we area group in computer science working in the design of distributed models of the brain, we are actually hostedin a biological and clinical environment, on the Neurocampus of the Bordeaux Hospital area. As such, ouractivity can be presented along two axes, corresponding to the impact of our models in neuroscience and incomputer science.

In association with Chile through the international ANR project KEOPS on the early visual system, wehave designed original retina models [AI94] in interactions with the thalamus and the cortex [CI71] thatallow them to handle natural scenes (outdoor) [SI6]. Concerning our insertion in the Bordeaux neurosciencecommunity which has a strong visibility in neurodegenerative diseases and addiction, we recently developedearly versions [CN3, AI79] of models of the amygdala, hippocampus and basal ganglia, neuronal structuresimplicated in both repondant and operant conditioning and in decision-making. From a more computationalperspective, we offer to our colleagues in neuroscience a solid expertise in the design of effective computationalmodels. For example, we recently reviewed a series of classical models of the basal ganglia (a neuronalstructure responsible for selection of action) in which we have pointed out some characteristics that arecritical for stable and reproducible performances. We are also beginning to study another critical feature,that of scaling to more realistically-sized information flows.

Our works also have more direct consequences in computer science. Our biologically inspired distributedarchitectures have intrinsically interesting computational properties, such as robustness to noise, self-organi-zation, on-line learning that we aim at better understanding. Finally, in addition to our early studies on theextension of classical models to large-scale models, we are transposing our expertise in distributed numericalcomputing, experimenting GPU programming [RI236] (vertex/fragment programming) that offers hardwareenforcement of distributed constraints: every fragment gets the same program but their combination pro-motes a global image effect.

On a short term perspective, we wish to merge these two lines of activity, designing biologically-inspiredmodels, useful for neuroscientists and studying them under realistic conditions in terms of distributed andlarge-scale computing. Recently accepted projects have been designed in that direction.

2.1.3 Scientific productionOur team has a recognized world-wide expertise attested by numerous publications in the best conferencesand journals: STOC, SODA, PODC, DISC, IPDPS, ICALP, STACS, EuroComb, ACM Transactions onAlgorithms (TALG), Algorithmica, Combinatorica, Discrete Applied Mathematics, Discrete Mathematics,Discrete Optimization, Distributed Computing, European Journal of Combinatorics, IEEE Transactions onParallel and Distributed Systems (TPDS), JCT-A, JCT-B, Journal of Algebraic Combinatorics, Journal ofComputer and System Sciences (JCSS), Journal of Graph Theory, Mathematical Programming Series Aand B, Random Structures and Algorithms, SIAM Journal on Discrete Mathematics (SIDMA), TheoreticalComputer Science (TCS), The Annals of Applied Probability, The Annals of Probability, ...

In the reference period, the team has published more than 250 papers in refereed international journalsand more than 190 papers in refereed international conferences with proceedings. Members of the team havealso co-authored 14 book chapters and 2 books. Finally, 9 HDR theses and 26 PhD theses were published.


Selected publicationsWe choose to present here some papers showing the wide range of interests of the team.

1. Ittai Abraham, Shiri Chechik, Cyril Gavoille. Fully dynamic approximate distance oracles for planargraphs via forbidden-set distance labels. STOC 2012 : 1199-1218.This paper considers fully dynamic approximate distance oracles in weighted planar graphs. We show howto maintain (1 + ε)-approximate distances in n-node planar graphs with distance queries and all node/edgeinsert/delete operations in worst-case time

√n (up to some poly-logarithmic factors). Best known solution

for the same problem had amortized complexity roughly n2/3. The solution extends to forbidden-set compactrouting scheme in planar graphs with poly-logarithmic routing tables and stretch 1 + ε.

2. Alvaro O. Ardiles 1, Cheril C. Tapia-Rojas, Madhuchhanda Mandal, Frédéric Alexandre, Alfredo Kirk-wood, Nibaldo C. Inestrosa, Adrian G. Palacios. Postsynaptic dysfunction is associated with spatialand object recognition memory loss in a natural model of Alzheimer’s disease. In Proceedings of theNational Academy of Sciences, August 2012, vol. 109, no. 34, pp. 13835-40.In this paper, we propose, by behavioral and electrophysiological studies, that the Degus (a rodent from Chile)could develop the Alzheimer disease and could be consequently an excellent animal model for this disease.

From its recent publication, this paper was already cited more than 20 times and was commented in manynewspapers, e.g.http://www.pourlascience.fr/ewb_pages/a/actu-un-modele-animal-naturel-pour-la-maladie-d-alzheimer-30278.php

http://www.alzforum.org/news/research-news/degu-debut-new-face-sporadic-alzheimers-research

3. Jean-Christophe Aval, Adrien Boussicault, Mathilde Bouvel, Matteo Silimbani. Combinatorics of non-ambiguous trees, Advances in Applied Mathematics 56 (2014) 78-108.This paper introduces and studies new combinatorial objects called non-ambiguous trees. New enumerativeresults, simple bijective proofs of known formulas, and a combinatorial interpretation of an integer sequencelinked to Bessel functions are obtained.

4. Nicholas R. Beaton, Mireille Bousquet-Mélou, Jan de Gier, Hugo Duminil-Copin, Anthony J. Guttmann.The critical fugacity for surface adsorption of self-avoiding walks on the honeycomb lattice is 1 +

√2.

Communications in Mathematical Physics 326 (2014) 727-754.Inspired by a recent breakthrough of Duminil-Copin and Smirnov on self-avoiding walks, a conjecture datingfrom 1995 is proved on the behaviour of such walks when they interact with a boundary.

5. Jérémie Chalopin, Emmanuel Godard, Yves Métivier. Election in Partially Anonymous Networks withArbitrary Knowledge in Message Passing Systems. Distributed Computing, 25(4):297-311, July 2012.Angluin asked in 1980 whether it is possible to characterize networks for which the leader election problem canbe done by a deterministic algorithm. This article answers positively to this question.

6. Louis Esperet, František Kardoš, Andrew King, Daniel Král, Sergey Norine. Exponentially manyperfect matchings in cubic graphs, Advances in Mathematics, 227(4): 1646-1664, 2011.In this work, an old conjecture of Lovász and Plummer (70’s) is proved: every cubic bridgeless graph G has atleast 2(|V (G)|/3656) perfect matchings.

7. Valentin Féray, Piotr Śniady. Zonal polynomials via Stanley’s coordinates and free cumulants. Journalof Algebra, 334 (2011), pp. 338-373.Zonal polynomials are a family of symmetric functions (a special case of Jack polynomials) which appear inrepresentation and random matrix theory. In this article, we give a new formula to express these polynomials interms of power sums, as a sum over matchings (or equivalently over graphs embedded in non-oriented surfaceswith a fixed face-degree distribution). This formula fits in the framework of polynomial functions over Youngdiagrams developed by Kerov and Olshanski and is used to prove particular cases of two conjectures of Lassalleon Jack polynomials.

http://www.pourlascience.fr/ewb_pages/a/actu-un-modele-animal-naturel-pour-la-maladie-d-alzheimer-30278.php

http://www.alzforum.org/news/research-news/degu-debut-new-face-sporadic-alzheimers-research


8. Juraj Hromkovič, Przemyslawa Kanarek, Ralf Klasing, Krzysztof Lorys, Walter Unger, Hubert Wa-gener. On the Size of Permutation Networks and Consequences for Efficient Simulation of HypercubeAlgorithms on Bounded-Degree Networks. SIAM Journal on Discrete Mathematics, 23(3): 1612-1645,2009.The sizes of permutation networks and planar permutation networks for special sets of permutations are in-vestigated. Several asymptotically optimal estimations for distinct subsets of the set of all permutations areestablished here. A consequence of our results is the construction of a 4-degree network which can simulateeach communication step of any hypercube algorithm using edges from at most a constant number of differentdimensions in one communication step in O(log logN) communication steps. An essential improvement ofgossiping in vertex-disjoint path mode in bounded-degree networks follows.

9. Adrian Kosowski. A O(n2) Time-Space Trade-off for Undirected s − t Connectivity. SODA 2013 :1873-1883.In this paper, we make use of the Metropolis-type walks due to Nonaka et al. (2010) to provide a faster solutionto the S-T -connectivity problem in undirected graphs (USTCON). As our main result, we propose a family ofrandomized algorithms for USTCON which achieves a time-space product of S · T = O(n2) in graphs with nnodes and m edges (where the O-notation disregards poly-logarithmic terms). This improves the previouslybest trade-off of O(nm), due to Feige (1995).

10. Mickael Montassier, Patrice Ossona De Mendez, André Raspaud, Xuding Zhu. Decomposing a graphinto forests. Journal of Combinatorial Theory, Series B, 102(1): 38-52, 2012.This works introduce a conjecture relating the fractional arboricity of a graph to its decomposition in forests.The conjecture is proved for two special cases.

Scientific productioninternational national

Peer-reviewed journals 250 1Contributed volumes 2Chapters in contributed volumes 13 2Editors of contributed volumes 5Invited conference talks 59 20Conferences with published proceedings 193 9Conferences without published proceedings 15 11Other publications 97 10Free software 4Completed PhDs (without cotutelle) 23Completed cotutelle PhDs 2 1Completed habilitations 9

2.1.4 Visibility and attractivityOur team has a recognized national and international visibility and attractivity. We present below somenotable achievements, thus demonstrating the place of our team in the national and international community.

Prizes and Distinctions

Distinctions

• Mireille Bousquet-Mélou was awarded the Charles-Louis de Saulses de Freycinet prize (biennial Academyof Sciences prize created in 1925, to encourage research in Mathematics), 2009.

• Mireille Bousquet-Mélou received the CNRS Silver Medal, awarded by the INSMI, 2014.

• Valentin Féray became a Laureate of the Peccot Foundation, Collège de France, 2012.


• Cyril Gavoille has been appointed as Junior Member at the “Institut Universitaire de France” (since2009).

• Adrian Kosowski was awarded the Witold Lipski Prize for Young Researchers in Computer Science,2009.

• Adrian Kosowski has become a member of the Young Scientists Academy of the Polish Academy ofSciences, 2012-2016.

• Alexandre Zvonkine has been nominated to the Gabriel Lamé chair at the University of Saint Peters-burg, 2014.

Top Citation Papers

• Top Citation Paper of Theoretical Computer Science in 2010 for the period 2005-2010 (PhilippeDuchon, Nicolas Hanusse): Could any graph be turned into a small-world?, Theor. Comput. Sci.355(1): 96-103 (2006)

• Bresar, Dorbec, Goddard et al., Vizing’s conjecture: a survey and recent results, Journal of GraphTheory, 2012 [RI72]This survey is the best top cited article published in Journal of Graph Theory for years 2012-2013:http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291097-0118/homepage/MostCited.html

Best Papers

• PODC 2010 (Adrian Kosowski et al.): How to meet when you forget: log-space rendezvous in arbitrarygraphs (presented at Best Paper Session)

• DISC 2011 (Corentin Travers et al.): Locality and Checkability in Wait-Free Computing [CI115]

• ICALP 2013, track C (Adrian Kosowski et al.): Fast Collaborative Graph Exploration [CI94]

Invited Talks

• Members of the team gave invited talks at important national and international conferences and work-shops, including: Algorithms and Permutations, CNRS ’STIC-Santé’ GDR day: “Computer Scienceand the Brain”, Enumerative Combinatorics, Formal power series and algebraic combinatorics, French-Chinese workshop in Computational Neuroscience, International Conference in Discrete Mathematics,International Conference on Graph Theory, Combinatorics and Applications, IWOCA, Journées deCombinatoire de Bordeaux, SIROCCO, Workshop on Combinatorial Physics, Workshop of the Compu-tational Neuroscience Network, Workshop on Graph Theory.

Editorial and organizational activities

Steering Committees

• Mathilde Bouvel is a member of the Steering Committee of the series of Conferences PermutationPatterns, since 2012.

• Cyril Gavoille is a member of the Steering Committee of the ACM Symposium on Principles of Dis-tributed Computing (PODC), 2009-2011.

• Ralf Klasing is a member of the Steering Committee of the International Colloquium on StructuralInformation and Communication Complexity (SIROCCO), since 2011.

Editorial Boards

http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291097-0118/homepage/MostCited.html


• Members of the team act as Associate Editor for important international journals, including: Advancesin Applied Mathematics; Algorithmic Operations Research; Annals of Applied Probability; Annales del’IHP D : Combinatorics, Physics and their Interactions; Computing and Informatics; DiscussionnesMathematicae Graph Theory; Discrete Applied Mathematics; Electronic Journal of Combinatorics; Fun-damenta Informaticae; IEEE Transactions on Parallel and Distributed Systems (TPDS); Journal ofCombinatorial Theory, Series A; Journal of Interconnection Networks; Kyungpook Mathematical Jour-nal; Networks; Parallel Processing Letters; RAIRO Theoretical Informatics and Applications; SéminaireLotharingien de Combinatoire; Theoretical Computer Science; Wireless Networks.

• Members of the team have been Guest Editor for special issues of important international journals,including: special issue of Theory of Computing Systems (2010) dedicated to the conference SPAA 2007;special issue of Discrete Mathematics (2009) dedicated to the conference ICGT 2005; special issue ofTheoretical Computer Science dedicated to the conference SIROCCO 2011; special issue of the Journalof Combinatorics dedicated to the conference Permutation Patterns 2013; Computing and Informatics.

• Members of the team have been Editor or co-Editor of the proceedings of important internationalconferences, including: ICALP 2010 (LNCS), PODC 2011 (ACM), SIROCCO 2011 (LNCS), SEA2012 (LNCS).

Program Committees

• Members of the team have acted as PC Chair or PC co-Chair of important international and nationalconferences, including: DYNAS 2010; BGW 2010; ICALP 2010; PODC 2011; SIROCCO 2011; FPSAC2011; BWIC 2011; SSS 2011 (Self-Stabilization track); IPDPS 2011 (Algorithms Track); GASCom2012; BGW 2012; SEA 2012; SSS 2013 (Ad-hoc, sensor, robot and opportunistic networks Track);ICPP 2013 (Algorithms Track); AofA 2014; BGW 2014; FCT 2015; Algotel 2012.

• Members of the team have acted as a member of the Program Committees of important interna-tional and national conferences, including: ADHOC-NOW, ALGOSENSORS, Algotel, BGW, Cap,CFSE, COCOA, COSI, CSE, CWPR, DIALM-POMC, DISC, DYNAS, Ecole Jeunes Chercheurs enthéorie des graphes, EMBS, ESA, EuroComb, Euro-PAR, FCT, FOMC, FPSAC, G-COM, HiPC,ICANN, ICALP, ICDCN, ICDCS, ICGT, ICPADS, IMAGINE, IPDPS, ISAAC, ISCIS, IWOCA, JDIR,Journées Graphes, MARAMI, MFCS, OPODIS, Parallel Data Mining, PODC, Riemann Surfaces andDessins d’Enfants, Roadef, SAB, SC, SEA, SIAM Conference on Discrete Mathematics, SIROCCO,SODA, SOFSEM, SSS, STACS, WALCOM, WG.

Conference Organization

• Members of the team have acted as Organization Chair or Organization co-Chair of important inter-national and national conferences, including: Annual meeting of the CNRS GDR “Multi-electrodes”(2013), BGW 2010, 2012, 2014, BWIC 2011, EuroComb 2009, ICALP 2010, NeuroComp 2012, Robots& Corps conference 2013, SEA 2012, SIROCCO 2011.

• Members of the team have acted as a member of the Organization Committees of important interna-tional and national conferences, including: Analysis of Algorithms 2014, Analytic Combinatorics 2011,Annual meeting of the CNRS GDR “Multi-electrodes” (2013), BGW 2010, 2012, 2014, BWIC 2011,EDA 2012, Enumerative Combinatorics 2014, EuroComb 2009, GASCOM 2012, ICALP 2010, JournéesALEA 2013, Journées combinatoires de Bordeaux (annually since 2009), Journées en l’honneur deRobert Cori (2009), Journées en l’honneur de Xavier G. Viennot (2012), NeuroComp 2012, Permuta-tion Patterns 2013, PODC 2010, Robots & Corps conference 2013, Sage-Combinat Days 2014, Schoolon Graph Theory 2013, SEA 2012, SIROCCO 2011, TERANET 2010, 2011, Workshop Cycles andColourings 2014.

In particular, we organized the following events:


• In 2010, we launched an international workshop in honour of André Raspaud, BGW (Bordeaux GraphWorkshop). This workshop was very successful and attracted an high quality international audience.We organized the second edition in 2012 and the third one will be next November: http://bgw.labri.fr

• The ”Journées de combinatoire de Bordeaux” (JCB), an annual conference (since 2009) where thespeakers are invited from all parts and groups of France, and a large space is given to PhD studentsand young researchers.

• Members of the team have been strongly involved in the organization of ICALP in Bordeaux in 2010,as the general co-chair of the conference, as chairs of some workshops, and also as local organizers withthe full support of INRIA and the LaBRI. This main scientific event, including six workshops, hadnearly 300 participants.

• Members of the team have been strongly involved in the organization of SIROCCO in Gdansk in 2011,e.g. as the Organization Chair.

• The International Bordeaux Workshop on Identifying Codes (BWIC 2011) was organized at the LaBRIin Bordeaux from 21st to 25th November 2011 within the framework of the IDEA project.

• The 11th International Symposium on Experimental Algorithms (SEA 2012) was organized at theLaBRI in Bordeaux from 7th to 9th June 2012.

• The European Conference on Combinatorics, Graph Theory and Applications (EuroComb 2009) wasorganized in Bordeaux from 7th to 11th September 2009.

• The annual symposium of the CNRS GDR “Multielectrodes” was organized in Bordeaux in October2013.

Scientific ResponsibilitiesMembers of the team have fulfilled important scientific responsibilities, including:

• Scientific Deputy of Inria Bordeaux Sud-Ouest, 2010-

• Head of the “Algorithms and Combinatorics” group within the GDR Informatique Mathématique;Co-Head of the “Graphs” group within the GDR Informatique Mathématique 2010-2013;Co-Head of the COA group within the GDR Informatique Mathématique since 2012

• Scientific Council of the INSMI (Institut national des sciences mathématiques et de leurs applications,CNRS)

• Scientific Council of the FSMP (Fondations des sciences mathématiques de Paris)

• Member of the Cocor ALLISTENE alliance

Editorial and organizational activitiesinternational national

Steering committee 3Program committee 107 15Chair of program committee 16 1Organizing committee (conferences, seminaries, schools...) 14 6Chair of organizing committee 4 1Journal editorial board 22Research animation 1 7

http://bgw.labri.fr

http://bgw.labri.fr


Service as expert or evaluator• Members of the team acted as members of scientific committees, including: “Commission NationalePES” (2009, 2010, 2012), Evaluation Committee of the programme “ANR DEFIS” (2009), Scientificcommittee of the CNRS PEPS program (2012, 2013), “Conseil national des universités” (2009-2012,since 2012).

• Members of the team acted as AERES experts for research labs, including: LIFO (Orléans, 2010),LIGM (Marne-la-Vallée, 2013), LINA (Nantes, 2010), LIPN (Paris Nord, 2012), LITA (Metz Univer-sity, 2011), LIX (Polytechnique, 2014), LRI (Paris XI University, 2013), PRISM (Versailles, 2013).

• Members of the team acted as experts for international and national research funding programs, in-cluding: ANR programme Jeunes Chercheurs, ANR programme ARPEGE, ANR programme blanc,ANR programme numériques, ANRT Cifre, Austrian Science Fund (Austria), Digiteo-DigiCosme, FondRecherche Quebec (Canada), ITMO “Neurosciences, Sciences Cognitive, Neurologie, Psychiatrie”, Na-tional PES 27e committee, NSA Mathematical Sciences Grants Program, NSERC/CRSNG (Canada),NSERC Discovery Grant (Canada), Projets Emergence (Mairie de Paris), Swiss National ScienceFoundation (Switzerland), US-Israeli Binational Science Foundation.

• Members of the team served on the hiring committee for (assistant/associate/full) professor positions inComputer Science and Mathematics in universities, including: Aix Marseille University, University ofBordeaux, University of Caen, University of Evry, University of Marne la Vallée, University of Geneva(Suisse), University of Paris 6, University of Picardie, University of Toulouse.

• Members of the team acted as a reviewer of an application for tenure and promotion to AssociateProfessor at universities, including: Memorial University of Newfoundland, Canada.

• Members of the team acted as reviewer of Ph.D./H.D.R. theses in international universities, includ-ing: Chalmers University (Sweden), Dalhousie University (Canada), Jerusalem University (Israel),University of Bologna (Italy), University of Freiburg (Germany). University of Melbourne (Australia),University of Potenza (Italy), University of Stockholm (Sweden), Université des Sciences et de la Tech-nologie Houari Boumédiène (Algérie), Université du Québec à Montréal (Canada), University CollegeDublin (Ireland), University of Turku (Finland), University of Vienna (Austria).

• Members of the team acted as a reviewer or jury member of more than 90 Ph.D./H.D.R. theses inFrance and abroad.

• Members of the team acted as members of juries, including: Jury du concours d’entrée des ENS(Informatique), Jury IUF junior, Jury member of the National Prix Specif of PhD thesis Gilles Kahn.

Service as expert or evaluatorinternational national

Membership in expert committee 1 27Individual expert (reviewer) 10Membership in selection board 3Membership in prize jury 1Reviewing of PhD or habilitation 13 55Membership of PhD/habilitation committee 2 26

Scientific collaborations

Research ProjectsInternational laboratories:


• LIA LIRCO 2011-2014 (overall coordinator): LIRCO (Laboratoire International Franco-Canadien deRecherche en Combinatoire) is a LIA, International Associated Laboratory, label awarded by the CNRS.The themes cover a broad spectrum of research in combinatorics (algebraic combinatorics, enumerativecombinatorics, combinatorics on words, ...) and several of its applications, some in bioinformaticsand information visualization. The LIRCO includes French and Quebec researchers. The Frenchcore of the LIRCO is at the LaBRI in Bordeaux, the Quebec kernel is at the LaCIM in Montreal.(http://lirco.labri.fr)

European projects:

• European project FP7 STREP “EULER” (2010-2014)

• European Cost 295 DYNAMO (2005-2009)

Associated teams and other international projects:

• Royal Society Grant with the University of Liverpool (2011-2013)

• GraTel, France/Taiwan-Bordeaux-Taipei-Kaoshiung (2010-2013)

• ECOS Sud-Conicyt project with Chile, about retina degeneration and neural models (2014-2016)

• CEFIPRA-CNRS project with India (U. Hyderabad) about the design of neuronal models related tothe Parkinson disease and their implementation at large scale (2014-2016)

National initiatives:

• ANR A3, ANR ALADDIN, ANR Alpage (overall coordinator), ANR Displexity, ANR DORSO (overallcoordinator), ANR EGOS, ANR IDEA (overall coordinator), ANR MARS (overall coordinator), ANRPSYCO (overall coordinator), ANR SADA (overall coordinator), ANR SONGS, ANR USS-SIMGRID

Clusters of excellence:

• LabEx CPU: The LabEx CPU is a cluster of excellence at the University of Bordeaux on “Digitalcertification and reliability”. (http://cpu.labex.u-bordeaux.fr)

• Labex BRAIN: The LabEx BRAIN (Bordeaux Région Aquitaine Initiative for Neuroscience) is a clusterof excellence at the University of Bordeaux on neuroscience research.(http://brain.labex.u-bordeaux.fr/)

Collaborations. The team has numerous (national and) international collaborations. More precisely, theteam has had more than 120 joint publications with international co-authors. It has had more than 40international visitors, including several senior and junior invited professors. Members of the team have hadmore than 40 invited international research visits.

Scientific collaborationsinternational national

Projects 16 10Joint publications 125Research visitors 43 6Research visits 40

2.1.5 Involvement with social, economic and cultural actorsCollaborations with the industryEven though the team is mainly involved in basic research, we also participated in industrial projects: SIMID(Aeronautics), STREP 7 European project “EULER” (Routing, with Alcatel-Lucent Bell), Investissementd’Avenir SPEEDDATA (Distributed Data Mining Computing, with AT-Internet).


Collaborations with the industrytotal

Industrial contracts 4

General audience actionsThe team has been actively involved with social, economic and cultural actors, as shown by the followingselected activities:

• Animation of workshops Maths à Modeler en Aquitaine

• Participation in the associative project Mat’les Vacances, http://paestel.fr/matlesvacances

• Animation of workshops Math.en.jeans

• Participation in the project science-info-lycée

• Interventions at schools

• Member of the Editorial Board of Interstices, http://interstices.info/

• Co-editor of Binaire, http://binaire.blog.lemonde.fr/

• Public Relations Officer of the LaBRI

• We participated on several occasions in “La fête de la science”, on topics like “volunteer computing”,“parallel computing” and “distributed routing”.

• Animation of workshops at the “Fête du LaBRI”

• Animation of workshops at Cap Science, Bordeaux

• We participated on several occasions in several local events like “Unité ou Café” (local events to presentresearch activities to scientific and non-scientific Inria employees), on topics like “the art of choosingthe right links” and “Seti@home and volunteer computing”.

• Editor-in-Chief of 1024, bulletin of the “Société informatique de France”

• Members of the Administrative Council of the “Société informatique de France”

• In January 2013, F. Alexandre participated in the program “Science Publique”, on the French nationalradio France Culture to a one-hour debate entitled “What can we expect from an artificial humanbrain?”

General audience actionstotal

Learned society, federation 2Scientific popularization, dissemination of scientific culture 28Publications for large audience 4

2.2. IMAGE AND SOUND 39

2.2 Image and Sound

2.2.1 Members

PR MCF CR DR TotalJanuary 1, 2009 8 12 4 0 25June 30, 2014 9 13 7 0 29

PhDs defended: 17On-going PhDs: 22Post-doctoral fellowships: 48 months

Staff (on 2014/06/30): BALDACCI Fabien (MCF), BARLA Pascal (CR), BENARD Pierre (MCF),BENOIS PINEAU Jenny (PR), BEURTON AIMAR Marie (MCF HDR, TAI theme leader), BLANC Carole(MCF), BRAQUELAIRE Achille (PR), BUGEAU Aurélie (MCF), COUPE Pierrick (CR), COUTURE Na-dine (PR), DESAINTE-CATHERINE Myriam (PR, SI theme leader), DESBARATS Pascal (PR, teamleader), DOMENGER Jean-Philippe (PR), FERON François-xavier (CR), GONZATO Jean-Christophe(MCF), GUENNEBAUD Gaël (CR), GUEORGUIEVA Stefka (MCF, AR theme leader), GUITTON Pascal(PR), HACHET Martin (CR HDR), HANNA Pierre (MCF), JOURNET Nicholas (MCF), LOTTE Fabien(CR), NICOLAS Henri (PR), REUTER Patrick (MCF), ROBINE Matthias (MCF), ROUAS Jean-luc (CR,deputy team leader), SCHLICK Christophe (PR), TA Vinh-Thong (MCF), VIALARD Anne (MCF)

Hired Postdocs (2009/01/01-2014/06/30): AMMANN Lucas (2010-2011), FOURER Dominique (2013-2014), HEGEDUS Ramon (2013-2014), BARKI Hichem (2011-2012)

PhD students (on 2014/06/30): ARIAS-ALMEIDA Jaime-Eduardo, BALDISSER Emeric, BEN AHMEDOlfa, BEN HAMIDA Amal, BENUREAU Fabien, BUSO Vincent, CHARTON Jérôme, DUTAILLY Bruno,EMILIEN Aurélie, FREDERIQUE Louis, FREY Jérémy, GERVAIS Renaud, IOANNIDIS Leonidas, KOM-LAGAN Mawulawoé, LAPEYRE Matthieu, MOUAWAD Pauline, NGUYEN-VU Ngoc Tung, PIERRE Fa-bien, RAYMOND Boris, REN Yi, RIDEL Brett, VINSONNEAU Emile

2.2.2 Scientific reportThe general goal of our research team is to develop methods to improve the acquisition, analysis, modeling,synthesis, and interaction with data that could be labeled as multimedia data. The data manipulated bythe team represent a wide spectrum from sound to 2D or 3D images and video. In the first years of thisquinquennal project, the team was structured into four themes, roughly covering the variability of thismultimedia data (sound, 2D and 3D discrete images, point clouds and meshes, video). Since september2013, the team is now organized into three themes: Acquisition and Rendering (AR), Sound and Interaction(SI) and Image Processing and Analysis (IPA), each theme being subdivided into research groups.

Theme AR: Acquisition and renderingKeywords: Instrumentation and Acquisition, Display Building and Control, 3D Computer Vision and

Calibration, Reconstruction.About 9 permanent researchers are involved in the "Acquisition and Rendering" theme, 7 of them also

belong to the INRIA project team MANAO. In the next we present a non-exhaustive vision of some resultsin acquisition, rendering and geometry processing for which members of our theme are recognised as leading-edge experts.

• Acquisition: acquisition and display of material appearance is a novel axis in our research correspond-ing to our close collaboration with the IOGS (Institute Optics Graduate School). The intersectionof optics and computer science provides a unique opportunity to develop new acquisition and displaytechnologies. A representative example of this work is the KaleidoCamera,a prototype setup to achieveHigh Dynamic Range, Multispectral and Light Field imaging.In the context of cultural heritage, 3D laser scanning and photogrammetric 3D acquisition of broken


content result in large collections of detailed fractured archaeological 3D objects. Major initiativeswithin this context are the ANR SeARCH project, the closer partnership with Archéovision and theparticipation in the European Network of Excellence V-Must.net. Theses projects lead to developmentof new interaction, geometric modeling and visualization techniques. Our main goal is to increaseefficiency and robustness of shape analysis and matching. An outstanding fact within this activity isthe design of a software for virtual reassembly of fractured archaeological objects, ArcheoTUI [RI97].Surface 3D laser scanning was also investigated in relation with the rapid prototyping [SI8] and ap-plications to the digital anthropology [CI81],computer-assisted surgical planning and cultural heritagepreservation.

• Rendering: we are interested in providing real time legible visualisation of shape and material charac-teristics of objects in animated 3D scenes.Bidirectional Reflectance Distribution Function models of real-word material are well established do-main in our team since the early nineties. Significant research is still directed to design more effi-cient representations suitable to simulate all complex phenomena involved in light reflection. RationalBRDF[RI88] provide a generic and compact representation for arbitrary BRDFs based on RationalFunctions. An optimization of this approach, the MicroSculpt, was presented at AFIG’2012, and wasacknowledged with the 3rd best paper award.In the context of expressive rendering, work is focused on the creation of stylization primitives toachieve line-based rendering or stylized shading with various levels of abstraction. Major result in thisfield is the Radiance Scaling [CI240], that received the best paper award at the 2010 Symposium onInteractive 3D graphics and games.Implicit Brushes have been introduced by [RI122] to render animated 3D scenes with stylized linesin real-time with temporal coherence. This work has won the 3rd best paper award at Eurographicsannual conference, 2011.The Surface Flow proposed by [RI119] further exploit differential analysis of radiance to create 3Dshapes and materials without simulating the physics of light transport.With respect to the legible depiction of relief features occurring at various scales, we should mentionthe Surface Relief Feature approach proposed in [RI3]. Further extended by the Grow Least Squaresmethod for multi-scale analysis presented at the Eurographics Symposium on Geometry Processing2012. This research was successfully applied for the design of the Revealing flashlight [CI216], an in-teractive spatial augmented reality setup, presented with a collaborative work on the Isis statue of6 months exhibition at the "Musée Royal de Mariemont" (Brussels, 2012), and a public exhibition"Eternal Egypt" at the Museum "Allard Pierson" in Amsterdam (the Netherlands, 2013).Outstanding results in rendering of dynamic 3D scenes are the Dynamic Stylized Shading Primitivesandthe Dynamic Solid Textures [CI48]. The Screen-Space Curvature, presented at "SIGGRAPH Talk pro-gram" 2013, is another example for real-time editing tool that exhibits temporal coherence with negli-gible performance overhead.In the context of real-time photorealistic rendering the challenge is to compute most plausible imageswith minimal effort. We can cite the Soft-Shadows Maps proposed by [RI5] for rendering visuallyplausible anti-aliased soft shadows based on perceptual resolution prediction metric, and on-line video-based visualization using Context Features in Augmented Reality [CI56]. Both examples show ourparticular interest to develop efficient solutions to trade the speed over the quality in rendering ofcomplex lighting phenomena.

• Modeling and geometry processing : we are concerned with geometric modeling of discrete surfacesapproximating surface boundary of synthetic or real 3D Objects.Reconstruction of valid object boundary from acquired 3D point set plays a key role in all computerassisted design and manufacturing applications. Our interest is directed in particular to discrete surfacemodel that are "printable" and do not exhibit singularities as non-manifold conditions, ill orientedboundary contours, self-intersections and degenerated geometries. With this respect our main resultis the reconstruction and 3D printing of the Trochlear surface [CI118] of a specimen collection fromPessac osteological repository in collaboration with UMR PACEA, A3P Team. The novelty of theproposed approach is that the 3D reconstruction and its 3D prototype comply with feature size linear


dimension of the original surface.We should cite also our work on the surface subdivision schemes, Least Squares Subdivision Surfaces[RI11], that offer much higher visual quality, especially in the vicinity of extraordinary vertices.The major result in our geometry processing activity is the Eigen project, that won the “High-qualitysoftware in geometry processing award” from the Symposium on Geometry Processing, 2013.

Theme SI: Sound and InteractionKeywords: 3D interaction, tangible interaction, brain-computer interfaces, virtual and augmented re-

ality, sound modeling close to perception, musical similarity, speech processing, prosody analysis, syntaxicanalysis

The main objective of the Sound and Interaction theme is the elaboration of new methods of interactionsbetween users ans digital worlds, especially 3D ones, and the description of sound, music and speech. Itsactivities are organized in three research axes : artistic creation, data navigation and interaction. Artisticcreation. Our interest is in computer-aided artistic creation, mainly in the field of music and live show.We develop new human-machine interactions and new real-time writing systems while studying the creativeprocess musicology.

• New real-time writing systems : we study the specification of time-line based interactive scenarios withconditionnal branching allowing the command of multimedia processes using formal models (Petrinetworks, NTCC, reactives langages).

• New interactions for live shows : show enhancement by speech, music or interactive movie control byemotions or interactive loops made from music analysis.

These works are led in the framework of SCRIME project (Studio de Création et de Recherche en Informa-tique et Musique Electroacoustique) and within ANR INEDIT and PEPS ISME projects.Data navigation. The objective is sound archives indexation et content retrieval. We develop new de-scriptors allowing data classification et we elaborate new content research means using musical similarityautomatical estimation.

• since 2010, under the « speech automatic processing », we deal mainly with voice expressivity.

• musical similarity : research and application of bioinformatics algorithms for musical sequences com-parison.

• descriptors conception : rythm, singing voice, musical structures (musical parts detection such aschoruses).

• voice style and singing styles characterizationfor automatic voice transcription on spontaneous voicedata.

• prosody modelisation for automatic language detection et comparative analysis of social affects expres-sivity on several languages.

This works led to the creation of Simbals company and are conducted within DIADEMS, PEPS Mavoix,Idex Seduction and international ANR MexCulture projects.Interaction. We explore new approaches for interaction between users and digital worlds, especially 3D,for various users : general public, artists, archeologists, industrials. Our work is organized following threeaxes:

• sensori-motor human capabilities understanding and interaction strategies design (work in collaborationwith cognitive science experts).

• interactive techniques design. This research axis deals with new software design for interaction tasks,mainly in 3D. This concerns also new interactive modalities using virtual and/or augmented reality,tangible interaction or brain-computer interfaces.


• exploring new usages and applications. We consider here interaction at a social and applicative level.We have a collaboration with Cap Sciences for testing new approaches within a LivingLab. We alsocollaborate with pedagogy specialists for education applications or with companies for industrialsapplications.

These interaction activities are conducted within the Potioc team (INRIA/UB/CNRS collaborative researchteam) and ESTIA’s interaction research group.

Theme IPA: Image processing and analysisKeywords: restoration, segmentation, features extraction, indexation, classification, information re-

trievalFrom image reconstruction to image analysis. IPA theme researches focus on the control of the

complete image processing chain: from image acquisition to high level analysis. We develop new methodsfor image reconstruction, filtering, segmentation and analysis, taking into account the image modality speci-ficities. The richness of our inter-disciplinary collaborations has allowed us to investigate several modalities:« natural images » (photography and video), biological and medical imaging (CT and micro-CT, MRI,ultrasound, confocal and multi-photon microscopy . . . ) and Non-Destructive Control techniques (such asTerahertz imaging). The strength of our theme is its ability to develop methods and algorithms for each linkof these processing chains while maintaining consistency for a given acquisition technique.Image reconstruction and processing. Significant results have been obtained by integrating imageprocessing operations within the image reconstruction step of the acquisition chain. For instance, in theDOTNAC European project (FP7), we have been able to develop ad-hoc acquisition/reconstruction tech-niques for 2D and 3D Terahertz aircraft inspection and for defect characterization in composite materials(in collaboration with LOMA). By integrating a discrete approach to the tomography techniques, we havealso improved the control over CT reconstruction methods (Benoit Recur’s PhD thesis, Region Aquitainebest thesis award 2010). These preliminary works have led to a collaboration with TomoAdour for the char-acterization and reduction of metal artifacts in tomography images (CIFRE PhD grant). Our theme alsodeals with image restoration and image enhancement. Recently, we proposed new technics for diffusion MRIdenoising and super-resolution in order to perform in-vivo high resolution DTI (Emergent Project TRAIL:“HR-DTI” ANR-10-LABX-57). These methods enable to get a new insight on the brain architecture and willbe applied on Alzheimer’s Disease (ANR Project MultlmAD; ANR-09- MNPS-015-01) and Multiple Sclerosis(InterLabex Brain-Trail-CPU Project) cohorts. Moreover, new methods for image and video inpainting andcolorization (Labex CPU PhD grant) have been designed by combining patch-based and variational meth-ods. Finally, we studied privacy preservation and proposed a method to anonymize a face while keeping theexpressions.

Image segmentation. IPA theme has a long experience in 2D and 3D image segmentation. Previousfundamental researches on 2D image structuring (based on discrete geometrical and topological models)has led to the creation and distribution of GIRL (General Image Representation Library) in the previousquadrennial. This work has been applied to the specific segmentation problem of the characterization of thehealing of wounds (in collaboration with the Urgo company - 3 year project). Moreover, the extension of thisstructuring model for the 3D case has led to the creation of a 3D segmentation framework (OBG – OrientedBoundary Graph). 3D segmentation is also performed on medical images using patch-based methods (foranatomical brain structure segmentation), snakes (for cardiac segmentation) or tubular structure identifica-tion (for bronchi or vessels segmentation). Recently, near real time patch-based method has been developedin our team for anatomical structures segmentation. This last advanced approach is currently integrated ina web-based service for remote online processing of MRI (http://volbrain.upv.es). This service is the resultof a long-term collaboration with the Polytechnic University of Valencia.

Image analysis. Analysis step uses classification algorithms and/or knowledge extraction methods.These methods have been applied for automatic evaluation of document image degradation and navigationinto big document images databases for instance (collaboration with BNF, I2S). On this media, analysis isalso used to provide information for synthetic generation of ground truth document images that can be usedfor benchmarking. Analysis is also used for the diagnosis of neurodegenerative diseases from MRI imagesor from the extraction of objects and gestures in complex video scenes taken from portative cameras. Animportant effort has been dedicated to Alzheimer’s Disease. Advanced features and new machine learningtechnics have been proposed in order to perform early detection of this pathology. These new computed-


aided diagnosis tools aim at helping the validation of potential new neuro-protective therapies. Moreover,when efficient medication will be available, such approach can help to offer a better-quality care for patients.These image analysis methods are developed in collaboration with several laboratories and Universities(RMSB, INCIA, IMS, IMB, McGill University, Polytechnic University of Valencia, . . . ) and companies (I2S,Gestform, Siemens, General Electrics, Philips, . . . ).

In the current team organisation, the IPA theme is composed of five groups: the AIV group (Analyse etIndexation Video - Video Analysis and Indexation) dealing with motion estimation, content indexation anddescription on video and medical images, the Document group which focuses its researches on document imageprocessing and analysis, the OS3D group (Outils pour la Segmentation 3D - Tools for 3D Segmentation) whoseinterest is to develop segmentation and analysis methods for 3D images, the MorphoBoid group which studiesautomatic classification of images based on image landmarks and the Pictura group which develops efficientimage processing algorithms (image segmentation, restoration, reconstruction, classification and editing).Note that OS3D and MorphoBoid groups were created whitin this year, which proves the adaptability of thecurrent team organisation.

2.2.3 Scientific productionOne of the strength of our team is the ability to address the whole chain of process on multimedia me-dia. This is reflected by our scientific production which includes reference publications and conferences invarious domains such as ACM Transactions on Graphics or Eurographics and SIGGRAPH conferences forComputer Graphics, IEEE Transactions on Audio, Speech and Language or Computer Music Journal forSound and Music processing, IEEE Transactions on Signal Processing and IEEE Transactions on ImageProcessing as well as IEEE International Conference on Image Processing for Image Processing and Anal-ysis. Our researches being multi-disciplinary, we also published in high quality journals and conferences inseveral domains: Physics (Optics Express, Optical Engineering), Medical Imaging (Medical Image Analysis,MICCAI, Journal of Magnetic Resonance Imaging,. . . ), Biology (EMJBIO), . . . Note that we also have astrong implication in patent registration (5 for this quinquennal, both national and international) and insoftware development.

In order to show the diversity of our activities, we have chosen 10 publications presented in the list below.

1. M. Desainte-Catherine, A. Allombert, G. Assayag. Towards a Hybrid Temporal Paradigm for MusicalComposition and Performance: The Case of Musical Interpretation, Computer Music Journal, Vol. 37,No. 2: p61–72, 2013.This paper presents the philosophical foundation of the time model interactive sheet music in thecontext of the interpretation and its formalism. This model defines a coherence between writtenaspects and interactive aspects of partition. The main idea is to define two supports time, the timelinefor editing, and the stream for execution and two kinds of events, static events (dated statically) andinteractive events (dated dynamically). Finally, temporal relationships can link two kinds of events, todetermine consistency between writing and execution.

2. M. Hachet, J.-B. De La Rivière, J. Laviole, A. Cohé, and S. Cursan. Touch-based interfaces for inter-acting with 3D content in public exhibitions, IEEE Computer Graphics and Applications, 33 (2013),pp. 80–85.This article presents new interactive approaches that increase user experience during visits to museums.Approaches are based on new designed devices, including Toucheo, PapARt and Cubtile. These devicesallow a direct interaction with 3D environments by means of touch-sensitive surfaces. Our experimentshave shown that such approaches had great potential among general public for mediation activities.

3. M. Toro, M. Desainte-Catherine, Camilo Rueda. Formal semantics for interactive music scores: aframework to design, specify properties and execute interactive scenarios. Journal of Mathematics andMusic, DOI:10.1080/17459737.2013.870610, 2014.This paper proposes a new semantics for partitions interactive graph based event to verify propertieson execution traces. It also offers a operational semantics based NTCC.


4. S. Boyé, P. Barla, G. Guennebaud. A Vectorial Solver for Free-form Vector Gradient, ACM Transac-tion on Graphics, Volume 31 Issue 6, Article No. 173 November 2012.A new vectorial solver for the computation of free-form vector gradients is introduced. Based on FiniteElement Methods (FEM), its key feature is to output a low-level vector representation suitable for veryfast GPU accelerated rasterization and close-form evaluation.

5. R. Vergne, P. Barla, R. Fleming, X. Granier. Surface Flows for Image-based Shading Design, ACMTransactions on Graphics, Volume 31 Issue 4, Article No. 94, July 2012.A novel method for producing convincing pictures of shaded objects based entirely on 2D image oper-ations is presented. This approach, called image-based shading design, offers direct artistic control inthe picture plane by deforming image primitives so that they appear to conform to specific 3D shapes.

6. R. Vaillant, L. Barthe, G. Guennebaud, M.-P. Cani, D. Rohmer, B. Wyvill, O. Gourmel, M. Paulin.Implicit Skinning: Real-Time Skin Deformation with Contact Modeling, ACM Transactions on Graph-ics, Volume 32 Issue 4, Article No. 125, July 2013.A real time method for character skinning, Implicit Skinning, is presented. The technique is a postprocess applied over a geometric skinning (such as linear blending or dual-quaternions) which handlesthe self-collisions of the limbs by producing skin contact effects and plausible organic bulges in real-time.

7. V. Rabeux, N. Journet, A. Vialard and J.-P. Domenger. Quality evaluation of degraded documentimages for binarization result prediction. International Journal on Document Analysis and Recognition(IJDAR), Volume 17, pp 125-137, 2014.This article proposes an approach to predict the result of binarization algorithms on a given documentimage according to its state of degradation. We characterize the degradation of a document image byusing different features based on the intensity, quantity and location of the degradation. The predictionmodels based on these features are used to select the best binarization algorithm for a given documentimage. Our methodology can be applied in the context of automated document image processing.

8. V.-T. Ta, R. Giraud, D.-L. Collins, P. Coupé. Optimized PatchMatch for Near Real Time and AccurateLabel Fusion. Medical Image Computing and Computer-Assisted Intervention - MICCAI, pp. 105-112,2014.In this paper, we introduce a new patch-based method using the PatchMatch algorithm to performsegmentation of anatomical structures. Based on an Optimized PAtchMatch Label fusion (OPAL)strategy, the proposed method provides competitive segmentation accuracy in near real time. Duringour validation on hippocampus segmentation, OPAL was compared to several state-of-the-art methodsand obtained excellent performance in terms of computation time and segmentation accuracy comparedto recently published methods.

9. S. Roujol, J. Benois-Pineau, B. Denis de Senneville, Mario Ries, Bruno Quesson, Chrit T. W. Moonen:Robust Real-Time-Constrained Estimation of Respiratory Motion for Interventional MRI on MobileOrgans. IEEE Transactions on Information Technology in Biomedicine 16(3): 365-374, 2012.This contribution is targeted on fine motion compensation in MRI sequences for image – guided ther-motherapy. This is a pluri-disciplinary research which has been conducted with CHU Bordeaux andis pursued now in collaboration with IHU LIRYC. The scientific contribution consists in introductionof a specific regularization term related to characteristic points detected on left ventricle in order tocompensation for the failures of motion estimation in case of occlusions due to the respiratory motion.

10. D. Szolgay, J. Benois-Pineau, Rémi Mégret, Yann Gaëstel, Jean-François Dartigues: Detection of mov-ing foreground objects in videos with strong camera motion. Pattern Anal. Appl. 14(3): 311-328, 2011.This paper is targeted on the detection of foreground moving objects in egocentric video recorded withcameras worn by patients with Alzheimer disease. The scientific contribution is in the introduction ofnew error measure of motion compensation, which takes into account aliasing effects on the bordersof static and moving objects and kernel-based classification framework for object separation in videoswith strong irregular motion.



Peer-reviewed journals 126 5Contributed volumes 3 2Chapters in contributed volumes 18Editors of contributed volumes 5 1Invited conference talks 11 4Conferences with published proceedings 248 25Conferences without published proceedings 21 12Other publications 33 17Patents 5Licensed software 11Free software 15Completed PhDs (without cotutelle) 17Completed cotutelle PhDs 2 1Completed habilitations 5

2.2.4 Visibility and attractivity

The visibility of the members of our team has allowed them to be involved in several invited talks in national(AFIG, AFRV, . . . ) and international (IPTA, ICPR, ICDAR, . . . ) reference conferences. This visibility isalso attested by the number of participations in PhD and habilitation committees (see table below). We alsohave received several distinctions including:

• Best paper award at the 2010 Symposium on Interactive 3D graphics and games for our paper “RadianceScaling for Versatile Surface Enhancement”.

• 1st prizes for ISBI Challenge, DTI and HARDI categories (E. Garyfallidis, S. St-Jean, M. Paquette,P. Coupé, M. Descoteaux. Constrained spherical deconvolution on signal and ODF values. ISBI’13 ).

• Region Aquitaine best PhD Award, 2011 (B. Recur).

• “High-quality software in geometry processing” prize et the 2013 Geometry Processing Symposium forthe Eigen library (linear algebra C++ template library).

Finally the attractivity of our team is attested by the appointment of 1 full professor, 4 assistant profes-sors, 2 CNRS CR2 researchers and 1 INRIA CR2 researcher during the last quinquennal.

Program committees, steering committees, organizing committees

The national and international visibility of our team is also attested by the vast number of participationsin editorial or organizing activities. Indeed the continuous implication of members of our team in programcommittees of reference conferences such as Eurographics or ICCV (including 2 national and 5 internationalprogram committees presidencies) and in journal editorial boards has been very important. Furthermore,the team has a strong implication in research animation by the presence of its members in various nationalassociations organizational boards (Association Française de Réalité Virtuelle, Association Francophoned’Interaction Homme-Machine, GDR STIC-Santé, GDR ISIS, . . . ).



Steering committee 5 1Program committee 50 3Chair of program committee 4 2Organizing committee (conferences, seminaries, schools...) 7 10Chair of organizing committee 2 1Journal editorial board 4 2Research animation 8

Service as expert or evaluatorMembers of our team have participated in a vast number of national and international PhD/habilitationcommittees. They are also strongly involved in hiring committees, being for University positions (profes-sors, assistant professors) or researchers (CNRS/INRIA) and engineers (IE/IR). They also served as expertsand/or evaluators for national programs as ANR, “Crédit Impôt Recherche”, PEPS or CIFRE. The inter-national visibility of some of our members allow them to participate as experts in international committeesas National Science and Engineering Council of Canada, United States-Isreal Binational Science Foundationor European programs.


Chair of expert committee 2Membership in expert committee 3Individual expert (reviewer) 10Chair of selection board 1Membership in selection board 9Membership in prize jury 6Reviewing of PhD or habilitation 7 39Membership of PhD/habilitation committee 2 42

Scientific collaborationsOur team is also involved in several national and international collaborations. Our researches beingmulti-disciplinary, members of our team participate or collaborate with local structures as Clustex CPU(http://cpu.labex.u-bordeaux.fr), Labex BRAIN (http://brain.labex.u-bordeaux.fr), Labex TRAIL (http://trail.labex.u-bordeaux.fr) or Labex LaScArBx (http://lascarbx.labex.u-bordeaux.fr/). We also participated in ANR pro-grams (Digidoc, Instinct, SeARCH, DIADEMS, DREAM, ALTA, Icos-HD, IMMED, TACIT) as well as othernational programs (PEPS, PEPI, PIA or FUI). Internationally, we are also involved in European Projects(PRISM, V-Must, DOTNAC, Demcare). One of our member is also involved in the French-Russian CNRSLIA K1812.


Projects 14 15Joint publications 35 24Other collaborations 8Research visitors 6 1Research visits 9 1

2.2.5 Involvement with social, economic and cultural actors


Collaborations with the industryThe activities of our team, from fundamental to applied research, has allowed to us to have collaborationswith the industry, with small companies (2S, Gestform, Image Guided Therapy, . . . ) or larger groups(Siemens Healthcare, General Electrics, . . . ). These collaborations have been materialized through projectsmentioned above (ANR, European projects, . . . ), CIFRE PhD grants or collaboration contracts. Note thatour activity in patent registration has led to the creation of the SIMBALS start-up (http://www.simbals.com)by members of our team (P. Hanna and M. Robine) and of a transfert cell linked to PACEA laboratory(http://www.vircopal.fr/).


Industrial contracts 6Contributions to professional journals and overview publications 3Reports for decision makers 2Collaborations outside of universities 8Start-ups 1

General audience actionsMembers of our team are strongly involved in general audience actions. These actions can be directed tostudents (with participation in several local programs for second degree students), professionals or generalaudience.

One of the originality of our team is the participation in art performance (SCRIME, Biarritz Ballets) andin Museums (with a permanent installation in the Allard Piearson Museum in Amsterdam for example).


Scientific popularization, dissemination of scientific culture 22Publications for large audience 15

2.3. FORMAL METHODS 49

2.3 Formal methods

2.3.1 Members

PR MCF CR DR TotalJune 1st, 2009 8 16 7 2 33June 30th, 2014 10 19 6 2 37


Staff (on 2014/06/30): BAUDERON Michel (PR), BILLAUD Michel (MCF), CARRERE Fréderique(MCF), CASTERAN Pierre (MCF), CLEMENT Lionel (MCF), COURCELLE Bruno (PR émérite), DICKYAnne (MCF), DURAND Irène (MCF HDR), FELIX Patrick (MCF), FLEURY Emmanuel (MCF), GAUWINOlivier (MCF), GIMBERT Hugo (CR), GLOESS Paul (PR), GRIFFAULT Alain (MCF), HERBRETEAUFrédéric (MCF), JANIN David (MCF HDR), LAPOIRE Denis (MCF), LEROUX Jerome (CR HDR),LOMBARDY Sylvain (PR), LY Olivier (MCF HDR), MOOT Richard (CR), MOSBAH Mohamed (PR),MUSCHOLL Anca (PR, team leader), MUSUMBU Kaninda (MCF), PLACE Thomas (MCF), PUPPISGabriele (CR), RENAULT David (MCF), RETORE Christian (PR, leader of axis “Logic and linguisticsin computer science”), ROLLET Antoine (MCF), SALVATI Sylvain (CR), SENIZERGUES Géraud (PR),SIMON Laurent (PR), SUTRE Gregoire (CR), VINCENT Aymeric (MCF), WALUKIEWICZ Igor (DR,leader of axis “Logic, languages and graphs”), WEIL Pascal (DR), ZEITOUN Marc (PR, leader of axis“Modeling and verification”)

Members of our team fulfill various administrative tasks at the level of LaBRI, the University of Bordeauxand IPB Enseirb-Matmeca. Among the main tasks: director of LaBRI (P. Weil), adjoint director of LaBRI(M. Mosbah) and head of “licence informatique” (M. Zeitoun).Postdoctoral researchers (2009/01/01-2014/06/30): BHATTACHARYA Sukriti (2013-2014), BRAUDLaurent (2011-2012), CLEMENTE Lorenzo (2011-2013), NGUENA-TIMO Omer (2009-2011, 2012-2013),PASQUALI Fabio (2014 –), PRAVEEN Manjunatha (2013-2014), TOTZKE Patrick (2014 –), WU Zhilin(2009-2010).PhD students (on 2014/06/30): BINDEL Sébastien, DUBOURG Etienne, HALFTERMEYER Pierre,KELMENDI Edon, KIRMAN Jérôme, PASSAULT Grégoire, ROUXEL Quentin, SYLVESTREMarc, TRANThanh Tung, VAN ROOIJEN Lorijn.

2.3.2 Scientific reportThe “Formal Methods” team has a large spectrum of scientific interests, with strong and internation-ally renowned expertise in automata and logic, language theory and grammars, graph decompositions,non-commutative algebras, distributed systems, infinite systems, extended logics and automata with data,weights, time, or probabilities. The focus of our research is on fundamental contributions in research areaswith significative potential for applications.

Till June 2014 the team consisted of three research axes “Logic, graphs and languages”, “Modelingand verification”, and “Logic and linguistics in computer science”. Taking into account the physical andthematical mobility of its members, since June 2014 the activities of the third axis have integrated theother two ones. This results in a team organized around two research axes of roughly the same size (ca. 20permanent researchers). These two axes have each a weekly seminar, where talks of high quality are presentedon a regular basis. A new seminar around the proof assistant Coq was launched in the academic year 2013/14.The team also hosts the project Rhoban, that designs autonomous legged robots, especially humanoid robots,and robots applied to precision farming. We are also involved in the transverse project VISIDIA/Dampas(jointly with CombiAlgo), that develops an environment for modeling and proving distributed algorithms.

The text below gives a synthetic presentation of selected results obtained by our team in the periodof reference. This presentation aims to show the impact of the results as well as the diversity of researchinterests of the team. This diversity has a common thread that consists in studying finite and infinite,discrete objects from a logical viewpoint, and manipulating them algorithmically. The common culture inour team is attested by joint publications, but also by the fact that the two main seminars of the team oftenattract members of all axes.


Axis “Logic, graphs and languages”

Logic and graphs. Combining the description of graph properties by MSO formulas and graph decompo-sitions is fruitful in two different domains: (1) the theory of graph grammars and graph transductions and(2) the construction of fixed-parameter tractable algorithms for checking MSO graph properties.

The book authored by B. Courcelle and J. Engelfriet [OI1] develops both aspects mentioned above ata fundamental level. In particular, tree- and clique-decompositions of graphs are formulated algebraically,leading to a presentation of context-free graph grammars as equation systems and to an algebraic view ofthe translation of MSO formulas into finite automata.

On the algorithmic side our team develops realistic model-checking applications for large graphs [RI34,CI77], based on the notion of fly-automaton. States and transitions of fly-automata are represented implicitlyby meta rules, instead of explicit listings in huge tables. Only those states and transitions are computedthat are required when running over a particular term describing the input graph. Some NP-completeproblems, such as coloring problems, can be solved in this way on relatively large graphs (> 1000 vertices).Besides their practical interest in model-checking, fly-automata can provide also a quantitative information,like computing the number of 3-colorings of a given graph. This opens further perspectives for using fly-automata for enumeration, optimization and counting problems. Another topic of future study are goodheuristics for computing graph decompositions. Reducing this problem to SAT offers interesting practicalperspectives that can exploit recent competences in SAT solving in the axis “Modeling and Verification”.

Logic and algebra. Deep insights into logical formalisms are obtained by studying limits of their expres-sivity. Algebra provides powerful methods for answering this type of problems. Historically it has been firstapplied to formalisms over words, but it has been extended to trees and other types of models.

Recently, our team has obtained an important breakthrough in one of the most classical problems of thisarea, open since the late nineties. The problem is to provide an effective characterization of classes of wordlanguages defined by quantifier alternation of first-order logic. We have shown such a characterization for thelevels up to Σ3, [CI216]. The new insight that allowed us this advance was to consider a more general, yeteffective problem, called separation problem. Indeed the separation problem serves as an intermediate stepbetween the levels of the hierarchy. In the future we aim at identifying relevant generalizations of separation,in order to solve them and to obtain decidability for other fragments, ideally for the full quantifier alternationhierarchy.

The algebraic viewpoint has been shown to be very fruitful in investigating several other logical andautomata settings, as the following examples illustrate. A decidable characterization of the quantifier-alternation hierarchy within two-variable first-order logic FO2 was obtained by means of a lattice of subvari-eties of the variety DA [CI153], which characterizes the logic FO2. For tree languages, the concept of forestalgebras was introduced and its basic theory was developed in [RI20], providing characterizations of manyinteresting tree logics. Forest algebras offer currently the most advanced general notion of recognizability fortree languages. Finally, the notion of recognizability has been developed for languages of labeled, bi-rootedtrees in [CI136], through the theory of inverse monoids.

Data formalisms. Data formalisms were originally motivated by applications in XML processing [RI19],and more recently by various settings that require an explicit reasoning about object identities (“nominals”),like parametric verification or analysis of programs with object creation. The need of reasoning effectivelyon properties of objects with data poses new challenges, such as designing regular-like formalisms that areexpressive, robust and algorithmically effective.

Various natural settings that handle data were investigated by our team. MSO with rigidly-guarded datatests was shown to be a robust logic for data words, as it corresponds to recognizability by orbit-finite datamonoids [CI84]. Data-walking automata over data words were shown to enjoy good algorithmic properties,in particular, both emptiness and inclusion are decidable for this model. We also settled the relationshipbetween deterministic, non-deterministic data-walking automata, and data automata, which is the modelthat captures two-variable logic over data words [RI18]. A further problem that we considered is containmentfor several fragments of Datalog over data trees [CI10], showing in particular decidability of containment forunranked data trees of bounded depth.

The medium term goals in this area are numerous. One of the main focus will be on two-way and unam-biguous register automata, hoping that the basic requirements of expressivity, robustness and algorithmic


effectiveness can be achieved.

Higher-order programs. We have worked on the analysis of higher-order functional programs using asan abstract syntax the λY -calculus, that offers an attractive alternative to variants of pushdown automata,or to that of recursive schemes. As the first witness of usefulness of this approach we have shown in [CI230]that an abstract machine for performing beta-reduction, called Krivine machine, is more suitable for model-checking higher-order programs than machines based on higher-order pushdown automata used before inthis context. Next, this approach has allowed us to generalize Muchnik’s theorem, that is a powerful toolfor proving decidability of theories [CI231]. Finally, we have shown that suitable variants of models for thelambda calculus offer an even more versatile approach than Krivine machines [CI232], although at presentthis technique is limited to properties expressed in weak monadic second-order logic.

In the short/medium term perspective we will concentrate on two directions: (1) extending the modelbased approach to bigger logical fragments, and (2) using the semantic approach to improve the algorithmicsof higher-order model checking. The first direction opens very interesting perspectives of interactions betweenthe semantics and the language theory communities. It may lead to a new theory encompassing the algebraictheory of regular languages, and extending it to finite and infinite trees. The second direction has alreadygiven us novel type systems for the model-checking problem, and many other promising aspects are waitingto be explored.

Weighted automata. Weighted automata were introduced in the sixties as a way to extend the expressivityof finite automata. More recently, they appear to be a cornerstone of the analysis of quantitative models.We studied the general framework of weighted automata on various semirings (usual numbers, min-plus,transducers,...) When ε-transitions are allowed, the number of computations on a given input are infiniteand therefore the definition of the behaviour of such an automaton requires stronger assumptions. We definedit in the framework of topological semirings [RI71], and showed in many cases that it is decidable whether thebehaviour of such a weighted automaton is well-defined. Our approach could be applied to other weightedmodels. We also worked on weighted two-way automata; we proved in [CI66] that, if the semiring of weights iscommutative, unambiguous weighted two-way automata can be emulated by unambiguous weighted one-wayautomata; we also showed that unambiguous weighted one-way automata can be emulated by deterministictwo-way automata.

From a different perspective and motivated by verification questions, we obtained Kleene-Büchi theoremsin the quantitative setting, by proving that a first-order calculus is expressively equivalent to 2-way walkingpebble automata. This was done both for words [CI47, RI21] and for abstract classes of graphs withreasonable properties [CI49], including trees, nested words, Mazurkiewicz traces and grids.

Axis “Modeling and verification”

Infinite-state systems. The reachability problem for Petri nets is an important research subject. Practicalalgorithms for this famous problem, that was solved by E. Mayr and R. Kosaraju in the mid eighties,remain a big challenge and would be extremely useful in many areas of program verification. We areworking towards a deeper understanding of the reachability problem, that may allow to progress on thealgorithmic side and open the venue for practical algorithms. We presented a new and simple algorithmfor the reachability problem [CI158, CI159], based on the existence of inductive Presburger invariants forexpressing non-reachability.

Semilinear Petri nets are nets where the reachability set is definable in Presburger arithmetics. They area very useful class of nets, since non-reachability witnesses are Presburger definable. We gave in [CI163] aneffective procedure based on acceleration for computing a Presburger formula describing the reachability setof semilinear nets. In particular, our tool FAST, that implements acceleration methods, is able to computethe reachability sets of semilinear nets.

Petri nets with an additional stack form a very interesting class of infinite-state systems: they are veryexpressive, and still it is conjectured that they can be analyzed algorithmically. For example, this extensionof Petri nets can directly model parametrized server-client systems where the server may use recursion andthe clients are finite-state. The main verification question, namely reachability, is open for this model formore than 15 years and is very challenging. We progressed recently on two other important questions about


this model, by showing that termination and boundedness are decidable [CI167]. As a short/medium termgoal we will consider the complexity of these two problems.

Distributed systems. There are still very challenging fundamental problems in this area, even for finite-state distributed systems. One such problem is to control one distributed system by another. We showed thatthe control problem for rendez-vous communication is decidable when the synchronization graph is acyclic,and that the complexity is non-elementary complete, even for reachability conditions [CI113]. This resultcomes as a surprise, since distributed control becomes undecidable in related models, e.g. the synchronousmodel of Pnueli and Rosner.

Synthesis of a finite distributed system from a specification is another topic where we progressed sig-nificantly. For general asynchronous automata we presented an optimal, exponential construction of asyn-chronous automata from deterministic finite automata [CI112]. In the case of acyclic synchronization graphswe obtained a simple, quadratic construction for asynchronous automata [RI64]. As a medium term per-spective we will investigate the synthesis problem for bounded communicating automata with acyclic com-munication graphs, along the lines of the previous construction.

We have also worked on richer models of communication as the one with unbounded communicationchannels. We have characterized precisely architectures with decidable reachability problem in [RI59], andprovided an analogous result for communicating, real-time systems in [CI72].

Probabilistic automata. Probabilistic automata are a natural extension of deterministic automata onfinite words with randomized events. These automata are very expressive, but from an algorithmic point ofview they are intractable: many natural decision problems (e.g., emptiness, universality, rationality, isolation)are undecidable.

The undecidability results have also consequences on the control of systems with partial observation.Indeed, when the observation is only partial, the best controllers are often randomized, for example Eth-ernet controllers use random delays to recover connectivity after a packet collision. As a consequence, thecomputation of optimal controllers reduces to undecidable questions about probabilistic automata.

Our team focused its research on a particular problem about probabilistic automata, called the value1 problem: are there words accepted by the given automaton with acceptance probability arbitrarily closeto 1? This question was open since the sixties, and we solved it negatively, showing that the problem isundecidable [CI116]. On the positive side, we designed a class of automata for which the value 1 problemis decidable [CI100], using algebraic techniques developed by Leung and Simon. We have extended thedecidability results to one player stochastic games [CI117] and numerous variants of the value 1 problem[CI99].

Real-time systems. Timed automata are finite automata extended with clocks whose values can becompared with constants and can be set to zero during transitions. The reachability problem asks if there isan execution of a given automaton reaching a given state. This is the core algorithmic problem in the analysisof timed automata for which a relatively efficient solution exists, thanks to abstraction methods allowingto deal with continuous values symbolically. We have managed to show that non-convex abstractions canbe used efficiently for the reachability problem [CI122, CI127]. Moreover, we have shown that one of theabstractions we have studied is in some precise sense the coarsest correct abstraction possible [CI126].

The improvements described above, together with new symbolic representations, make the real-timeaspect so manageable that the discrete state part becomes the dominant complexity factor in real-timereachability-checking algorithms. We think that the most promising direction to get the next order ofmagnitude improvement in efficiency will be to introduce partial-order methods to real-time verification.The other problem we want to tackle is verification of Büchi conditions for timed systems. Despite the factthat timed systems have been studied for about 20 years, there in not much progress in these two naturaldirections, and indeed there are some fundamental difficulties that need to be overcome.

Tools. The most mature tools developed in our team are the verification tool for finite-state systems AltaRicaand the SAT solver Glucose.

The modeling language AltaRica has been designed at LaBRI at the end of the nineties. The languageand an associated suite of tools became gradually well-known in the aerospace industry. A variant of thelanguage is used in commercial tool OCAS developed by Dassault. It is also an input language of the toolSIMFIA of EADS. In the period of reference we worked on a new kind of analysis, failure diagnosis. This


work was supported by a contract with Thales Avionics Toulouse and a CIFRE PhD thesis, and has beenimplemented in the ARC tool [CI151].

The award winning SAT solver Glucose was co-designed by L. Simon, recruited in September 2013 as aprofessor at IPB. During the first months at the LaBRI, the work on Glucose continued by studying modernSAT solver performances [CI204] and the parallelization of Glucose [CI22].

In addition to the core SAT research, new applications of SAT solvers for model checking and verificationwill be targeted. The main idea will be to mix the BDD approaches used in Altarica with the use ofincremental SAT solving technologies. This could allow to solve larger problems by balancing the effortbetween CPU-intensive (SAT oracles) and memory-intensive (BDD) demands.

A couple of further important software projects of our team can be mentioned. The following list isby no means exhaustive, it is meant to illustrate the diversity of our projects. TChecker is a new toolthat implements the abstraction techniques for timed systems mentioned above and is freely available since2014. A comparison between TChecker and the reference tool Uppaal showed better performance of TCheckeron several Uppaal benchmarks. LALBLC is a prototype tool checking the equivalence of two deterministicpushdown automata, [CI121]. It has been already employed in the verification of cryptographic protocols byresearchers at LORIA. The Vaucanson platform [CI87] is a C++ library dedicated to the computation withweighted automata, where the semiring of weights can be parametrized by the user.

Axis “Logic and linguistics in computer science”The group on logic and linguistics, by now dissolved, was focusing on several aspects of natural language,namely syntax and semantics. The mathematical models we use are logic, type theory, lambda calculus andformal grammars, and the convergence of the last two concepts is known as abstract categorial grammars.

The study of grammar formalisms underlying natural language syntax is of primary interest in our group.We have successfully applied algorithms for solving Datalog queries to the parsing of formal languages [CI42],in particular for the ones that correspond to human languages, namely mildly context sensitive languages.This latter class of languages has also been studied in connection with simply typed lambda calculus throughAbstract Categorial Grammars, and through First Order Linear Logic [CI185, AI39].

Obtaining better approximations of human language by formal languages is one of the basic researchthreads of language theory since its beginnings. The language MIX is a completely “unstructured” language,and is a standard example of a language that should not belong to a reasonable class of languages intendedto model human languages. Contradicting common beliefs we proved in [RI85] that MIX falls into theclass of Multiple Context-Free Languages. This class was widely believed to be the class of formal languagesapproaching most adequately human languages. Interestingly, the proof requires some exotic tools pertainingto algebraic topology.

The group pursued its work on categorial grammars, that represent a natural interface between syntaxand semantics — they can also recover some aspects of the Chomskyan syntax [RI7]. The textbook [OI2]gathers classical results about categorial grammars, as well as the linear logic view that was developed by ourgroup. Different ways of semi-automatically extracting categorial grammars from annotated treebanks havebeen investigated: a classical grammar extraction method [CHI7, CI183], as well as a novel approach usingtree transducers [CI233]. The extracted grammars have been used for a wide-coverage parsing of Frenchtext. What makes this wide-coverage parser interesting is that it produces a logical representation of themeaning of the sentence it has analyzed [CI184, RI74].

We introduced the semantic framework named the Montagovian generative lexicon (MGL) [RI10, AN8]which is a way to include lexical meaning into compositional semantics, computing the logical formulasassociated with a sentence. The MGL uses second-order typed lambda calculus (system F) enriched withcoercive subtyping [CI227] and the formulas that represent meaning are higher-order many-sorted formulas.We defined and used this framework to model the adaptation of word meaning to the context of utterance,and to give a proper account of lexical semantics and pragmatics: meaning transfers, possible and impossiblepredications and copredications, [RI10, AN8, CI227] fictive motion and deverbals [CI187, CI223]. The grouphas also shown its relevance for classical issues in compositional semantics, like verbal tense [CI157], pluralnoun phrases [CI180], quantifiers and determiners (with typed Hilbert operators) [RI81, II15, CI225].

On the practical and empirical side of computational linguistics, our group continued to develop thecategorial parser Grail [CI184, RI74] and the Lexical-Functional Grammar parser XLFG.


2.3.3 Scientific productionOur research activities have a broad spectrum and are attested by publications of high quality in the bestconferences in our domains: ICALP (International Colloquium on Automata, Languages and Programming),LICS (Symposium on Logic in Computer Science), STACS (International Symposium on Theoretical Aspectsof Computer Science), CAV (Computer Aided Verification), CONCUR (Concurrency Theory), FSTTCS(Foundations of Software Technology and Theoretical Computer Science), POPL (Symposium on Principlesof Programming Languages), TACAS (Tools and Algorithms for the Construction and Analysis of Systems),as well as journals of high reputation: Information and Computation, Logical Methods in Computer Science,Theoretical Computer Science, etc. Members of the group have co-authored two textbooks: Graph structureand monadic second-order logic, a language theoretic approach (B. Courcelle and J. Engelfriet, CambridgeUniversity Press 2012) and The logic of categorial grammars: a deductive account of natural language syntaxand semantics (R. Moot and C. Rétoré, Springer 2012). The team is currently developping 11 software tools.

We chosed in the list below 10 publications of the team showing the broad thematical focus.

1. B. Courcelle and I. Durand. Automata for the verification of monadic second-order graph properties.Journal of Applied Logic, 10:368–409, 2012.

The model-checking problem for monadic second-order logic on graphs is fixed-parameter tractable with respectto tree-width and clique-width. The proof constructs finite automata from monadic second-order sentences.These automata recognize the terms over fixed finite signatures that define graphs satisfying the given sentences.However, this construction produces automata of hyper-exponential sizes, and is thus impossible to use themin practice. To overcome this difficulty, we propose to use fly-automata, where transitions are described byprograms instead of tables. Using fly-automata, we can check effectively certain monadic second-order graphproperties with limited quantifier alternation depth, that are nevertheless interesting for Graph Theory. We giveexplicit constructions of automata relative to graphs of bounded clique-width, and we report on experiments.

2. E. Filiot, O. Gauwin, P.-A. Reynier, and F. Servais. From two-way to one-way finite state transducers.In 28th Annual ACM/IEEE Symposium on Logic in Computer Science (LICS), pages 468–477. IEEEComputer Society, 2013.

This paper addresses the following definability problem: given a function defined by a two-way finite statetransducer, is it definable by a one-way finite state transducer? By extending Rabin and Scott’s proof fromfinite automata to transducers, we show that this problem is decidable. Our procedure builds a one-waytransducer, which is equivalent to the two-way transducer, whenever one exists.

3. H. Gimbert and Y. Oualhadj. Probabilistic automata on finite words: Decidable and undecidableproblems. In 37th International Colloquium on Automata, Languages and Programming (ICALP),pages 527–538, 2010.

This paper considers algorithmic problems for probabilistic automata on finite words. Among these problems,the decidability of the value 1 problem was an open question since decades. We show that the value 1 problemis undecidable. Moreover, we introduce a new class of probabilistic automata, #-acyclic automata, for whichthe value 1 problem is shown to be decidable.

4. F. Herbreteau, B. Srivathsan, and I. Walukiewicz. Better abstractions for timed automata. In LICS- 27th Annual ACM/IEEE Symposium on Logic in Computer Science - 2012, pages 375–384. IEEE,2012.

A standard solution to the reachability problem for timed automata involves computing a search tree whosenodes are abstractions of zones. These abstractions preserve underlying simulation relations on the state spaceof the automaton. For both effectiveness and efficiency reasons, they are parametrized by the maximal lowerand upper bounds (LU-bounds) occurring in the guards of the automaton. We consider an abstraction definedby Behrmann et al. Since this abstraction can potentially yield non-convex sets, it has not been used inimplementations. We prove that this abstraction is the biggest abstraction with respect to LU-bounds that issound and complete for reachability. We also provide an efficient technique to use it to solve the reachabilityproblem.


5. J. Leroux. Vector addition system reachability problem (a short self-contained proof). In Principles ofProgramming Languages, POPL’11, pages 307–316. ACM, 2011.

The reachability problem for Vector Addition Systems (VASs) is a central problem of net theory. The generalproblem is known to be decidable by algorithms exclusively based on the classical Kosaraju-Lambert-Mayr-Sacerdote-Tenney decomposition (KLMTS decomposition). Recently from this decomposition, we deducedthat a final configuration is not reachable from an initial one if and only if there exists a Presburger inductiveinvariant that contains the initial configuration but not the final one. Since we can decide if a Preburgerformula denotes an inductive invariant, we deduce from this result that there exist checkable certificates of non-reachability in the Presburger arithmetic. In particular, there exists a simple algorithm for deciding the generalVAS reachability problem based on two semi-algorithms. A first one that tries to prove the reachability byenumerating finite sequences of actions and a second one that tries to prove the non-reachability by enumeratingPresburger formulas. In this paper we provide the first proof of the VAS reachability problem that is notbased on the KLMST decomposition. The proof is based on the notion of production relations, inspired fromHauschildt, that directly proves the existence of Presburger inductive invariants.

6. M. Bojanczyk, C. David, A. Muscholl, T. Schwentick, and L. Segoufin. Two-variable logic on datawords. ACM Transactions on Computational Logic, 12:27, 2011.

This paper shows that satisfiability for the two-variable fragment of first-order logic with data equality test, isdecidable over finite and over infinite data words. The satisfiability problem is shown to be at least as hard asreachability in Petri nets. Several extensions of the logic are considered, some remain decidable while some areundecidable.

7. T. Place and M. Zeitoun. Going higher in the first-order quantifier alternation hierarchy on words.In ICALP, International Conference on Automata, Languages, and Programming, volume 8573, pages342–353. Springer, 2014.

This paper investigates the quantifier alternation hierarchy in first-order logic on finite words. Levels in thishierarchy are defined by counting the number of quantifier alternations in formulas. We prove that one candecide membership of a regular language to the levels BΣ2 (boolean combination of formulas having only 1alternation) and Σ3 (formulas having only 2 alternations beginning with an existential block). Our proof worksby considering a deeper problem, called separation, which, once solved for lower levels, allows us to solvemembership for higher levels.

8. S. Salvati. MIX is a 2-MCFL and the word problem in Z2 is solved by a third-order collapsiblepushdown automaton. Journal of Computer and System Sciences, to appear 2014.

The language MIX is a completely “unstructured” language, and is a standard example of a language thatshould not belong to a reasonable class of languages intended to model human languages. We show here thatMIX falls into the class of Multiple Context-Free Languages. This class was widely believed to be the class offormal languages approaching most adequately human languages.

9. M. Bojanczyk, H. Straubing, and I. Walukiewicz. Wreath products of forest algebras, with applicationsto tree logics. Logical Methods in Computer Science, 8(3):1–39, 2012.

We use the recently developed theory of forest algebras to find algebraic characterizations of the languages ofunranked trees and forests definable in various logics. These include the temporal logics CTL and EF, andfirst-order logic over the ancestor relation. While the characterizations are in general non-effective, we areable to use them to formulate necessary conditions for definability and provide new proofs that a number oflanguages are not definable in these logics.

10. M. Kufleitner and P. Weil. - The FO2 alternation hierarchy is decidable - Computer Science Logic(CSL’12) - 26th International Workshop/21st Annual Conference of the EACSL 16 (2012) 426-439.

We consider the two-variable fragment FO2[<] of first-order logic over finite words. Restricting the number ofquantifier alternations yields an infinite hierarchy. We show that each level of this hierarchy is decidable. For


this purpose, we relate each level of the hierarchy with a decidable variety of finite monoids. Our result impliesthat there are many different ways of climbing up the FO2[<]-quantifier alternation hierarchy: deterministicand co-deterministic products, Mal’cev products with definite and reverse definite semigroups, iterated blockproducts with J-trivial monoids, and some inductively defined omega-term identities. A combinatorial tool inthe process of ascension is that of condensed rankers, a refinement of the rankers of Weis and Immerman andthe turtle programs of Schwentick, Thérien, and Vollmer.


Peer-reviewed journals 91 2Contributed volumes 3Chapters in contributed volumes 9 2Editors of contributed volumes 8 1Invited conference talks 20Conferences with published proceedings 240 10Conferences without published proceedings 8 1Other publications 58 7Free software 11Completed PhDs (without cotutelle) 19Completed cotutelle PhDs 3Completed habilitations 2

2.3.4 Visibility and attractivityThe quality and impact of the results obtained in our team is attested by a large number of invited lecturesat conferences that are references in our domain (CONCUR, FST&TCS, MFCS, . . . ) and of tutorials atinternational PhD schools (cf. list in the appendix4). The following national and international awards havehonored several members of our team:

• ACM Software System Award 2013 for the Coq proof assistant (P. Castéran)

• Best paper award at the Alan Turing centenary conference Turing‘100, June 2012 (J. Leroux)

• Silver medal CNRS 2010 (A. Muscholl)

A strong indicator for the attractivity of our team is the appointment of two full professors (S. Lombardy2012 and L. Simon 2013), two assistant professors (O. Gauwin 2011 and Th. Place 2012), one CNRS CR1researcher (G. Puppis 2012) and one CNRS CR2 researcher (D. Figuiera 2014).

Editorial and organizational activitiesInvolvement in organization and evaluation of scientific activity has been very considerable. Members ofour team are active in numerous editorial boards, among which there are prestigious journals like LogicalMethods in Computer Science, Information and Computation and Theoretical Informatics and Applications.

Our team is represented on a regular basis in program committees of the main conferences in our domains(ICALP, LICS, STACS, ETAPS, . . . ) and has chaired program committees of high-quality conferences likeESSLII’09 and FoSSaCS’14. Several members are active in steering committees of first-rate conferences likeSTACS (International Symposium on Theoretical Aspects of Computer Science), FoSSaCS (InternationalConference on Foundations of Software Science and Computation Structures) and ICGT (International Con-ference on Graph Transformation). Involvement in networking activities is strong, in national organizationslike GDR “Informatique-Mathématique” and “Génie de la Programmation et du Logiciel”, and internationalorganizations (IFIP WG2.2 Formal description of programming concepts).

4The invited talks in the table account only for talks with a contributed paper in the proceedings.



Steering committee 9 2Program committee 66 5Chair of program committee 5Organizing committee (conferences, seminaries, schools...) 5Chair of organizing committee 11Journal editorial board 11 3Research animation 1 2

Service as expert or evaluatorMembers of the team served in hiring committees of several French universities, such as U. Aix-en-Provence,U. Marne-la-Vallée (Paris-Est), U. Paris Diderot (Paris 7), U. Paris 13, U. de Lorraine, U. Paul SabatierToulouse. They acted as members of AERES evaluation committees of laboratories such as IBISC, LIP6, LIXand LORIA, and belong to the Conseil national des universités (CNU, 2011-2015) and Conseil scientifiqueINSII (2010-2014, president). They served as reviewers for research agencies of various countries (Austria,Canada, Germany, Israel, Netherlands, Switzerland, USA) and for international PhD and habilitations(Czech Rep., Germany, India, and Poland). They are members of international prize juries for the EATCSFellowship Committee and the Witold Lipski Prize.


Chair of expert committee 1Membership in expert committee 30Individual expert (reviewer) 10Membership in selection board 3Membership in prize jury 3 2Reviewing of PhD or habilitation 8 26Membership of PhD/habilitation committee 6 37

Scientific collaborationsOur team is involved in a large number of national and international cooperations. Locally, there aretraditionally strong links with the team “CombiAlgo” attested, among others, by the VISIDIA/Dampasproject. Several members of our team collaborate actively with many first-rate laboratories in France. Inparticular, 10 ANR projects started since the beginning of the evaluation period. The team has coordinatedseveral bilateral projects and has a longstanding collaboration with Indian IITs and other research institutes,attested in particular by the INdo-French FORmal MEthods Lab (LIA Informel) and the Franco-Indian ICSTproject AVeRTS (2014-2018).


Projects 7 14Joint publications 39 30Research visitors 16Research visits 22

2.3.5 Involvement with social, economic and cultural actors


Collaborations with the industryCollaboration with industrial partners is organized via ANR projects as well as through direct contracts. TheAltaRica project offers a modeling language and a set of tools, well-known in the aero-space industry. In theperiod of reference AltaRica had a contract with Thales Avionics Toulouse and a CIFRE PhD on diagnosisof avionic systems. Three other CIFRE PhD thesis with SERMA, EADS and 2Moro were supervised inour team within the project VISIDIA/Dampas. The project Rhoban collaborates with VITIROVER SAS,France within the EU project VVINNER (Vineyard Vigilant & INNovative Ecological Rover, 2012-2015).The start-up Rhoban System S.A.S was created in 2012.


Industrial contracts 2Collaborations outside of universities 2Start-ups 1

General audience actionsInvolvement with social and cultural actors is attested by a wide spectrum of activities in the period ofreference: participations at “Maths en jeans” and “Fête de la science”, presentations at general audienceexhibitions at Cap Science (Bordeaux, 2009), "Mathématiques, un dépaysement soudain" (Fondation Cartier,Paris, 2011) and the International exhibition EXPO 2012 (Yeosu, Korea 2012, French pavillon), participationat the international competition Robocup 2014 (Bresil). A Summer School around the Coq Proof Assistanttakes place in Shonan, Japan, August 2014.


Learned society, federation 1Scientific popularization, dissemination of scientific culture 18Publications for large audience 2

2.4. MABIOVIS 59

2.4 Modèles et Algorithmes pour la Bioinformatique et la Visu-alisation d’informations (MaBIOVIS)

2.4.1 Members



Staff (on 2014/06/30): ALLALI Julien (MCF), AUBER David (MCF HDR, responsable d’équipe avant07/2014), BLIN Guillaume (PR, après 08/2014), BON Elisabeth (MCF), BOURQUI Romain (MCF, respons-able du thème Evadome), DE DARUVAR Antoîne (PR), DELEST Marie-Pierre (PR), DULUCQ Serge (PR),DURRENS Pascal (CR HDR), DUTOUR Isabelle (MCF, responsable du thème CoBALT avant 07/2014),FERRARO Charles Pascal (MCF HDR), GIOT Romain (MCF), MAABOUT Sofian (MCF), MELANCONGuy (PR, responsable d’équipe après 08/2014), NIKOLSKI Marie (CR HDR), PINAUD Bruno (MCF),SHERMAN David (DR), THEBAULT Patricia (MCF), URICARU Raluca (MCF)

PhD students (on 2014/06/30): BOURGEADE Laetitia, BROEKSEMA Albertus, HUME Thomas,ISSA Razanne, RUDEWICZ Justine, SANSEN Joris, SCHMITT Louise-Amélie, VALLET Jason, ZHUKOVAAnna

Hired Postdocs (2009/01/01-2014/06/30): Witold Dyrka (2012-2014), Sébastien Rufiange (06/2013-06/2014)

2.4.2 Scientific reportScientific activitiesThe team MABioVis develops a scientific vision inspired by the synergy now taking place between in-formation sciences, life sciences, social sciences and economics. The combination of experimental tech-niques for high-speed and advanced computational methods allows to tackle problems of unprecedented size,and gives birth to scientific issues emerging in a va-riety of fields such as biology and quantitative ge-ography. In the different areas that we study, thedata can be modeled by complex systems defined assets of interacting entities. Members of the MABio-Vis team contribute to the development and study offormalisms, models and algorithms providing resultson both extraction and data management, but alsoon the construction, analysis and understanding ofthese complex systems. The results obtained and theties with academic and industrial partners show thatwe have been successful at addressing this challengein biology (life systems) and quantitative geography(urban networks).


Team organizationOn its own initiative, the team conducted a mid-termreview in May 2013, and has benefited from the visit of external scientific experts. This evaluation indicatedthat its organization seemed unbalanced with a breakdown into three themes benefiting bioinformatics.Following this evaluation, the team re-organized into two themes T1 and T2:

• T1- Computational Biology, CoBalt (theme leader Isabelle Dutour)Keywords: Integrative biology, genomics, comparative genomics, systems biology, biological networks,RNA, NGS, Multi-scale modeling stochastic biological process

• T2- Visual Analytics and Interactive Exploration of Massive Data, EVADoM (theme leader RomainBourqui)Keywords: Information Visualization, Massive Data, Databases, Graph Algorithms and Graph Draw-ing, Interactive Manipulation of Graphs, Visual Analytics

The synergies between our two themes exist at different levels. Problems emerging form the differentapplication domains we investigate share similarities – biology, social sciences and economics, among others.We devote our efforts in two main directions: on the formalization of complex systems, and on the develop-ment of computational strategies and algorithms targeted at complex systems. In practice, this results inthe pooling of multi-disciplinary competencies and expertise of the team. Our weekly working session andcollaborations between members of the two themes favor the development of a common vision and scientificculture, with shared experience and know-how. The variety of our research allows us to communicate andpublish towards a wide audience. For example, in computer science, our work has been published in majorinternational conferences such as EuroVis, IEEE InfoVis, ACM CIKM, FOLKS, CMSB, GECCO and inthe most prestigious journals such as Computing, Transactions on Visualization and Computer Graphics(TVCG) and Bioinformatics, Nucleic Acids Research and Nature Biotechnology.

Computational Biology – CoBaltThe research conducted in CoBalt takes its source in many areas in biology or bio-informatics and from bio-logical data: genomic and protein sequences, RNA, biological interaction networks, metabolic and signalingpathways. We aim at the development of new algorithms and formal models for the analysis of genomes,networks, and more generally the study of complex systems. We ultimately support biologists in their un-derstanding of the structure and the history of genomes. We thus address challenges initiated from problemsin bioinformatics while encompassing issues in computer science: algorithmic recognition and inference pat-terns, data mining and classification, modeling of complex dynamical systems, prediction and comparisonof networks, comparative genomics in a broad sense. Our activities are twofold as detailed in the followingparagraphs..

Coding, processing and analysis of biological dataA common denominator of the work carried by members of CoBalt is the exploitation and analysis of

biological data, tackled from different angles. A first concern is the transformation of data obtained from newsequencing technologies (NGS) into assembled biological sequences, with the assembly quality as a key factorfor the exploitation of results. Mix [RI82] contributes to this problem and offers a method relying on thecomputation of a graph capturing how genome segments have been pieced together. We also considered thesimultaneous use of data from multiple metagenomics agencies to improve a taxonomic assignment algorithm(through a collaboration with a team from Barcelona) [RI61].

The annotation of genomic data can be tackled by either combining various bioinformatics approachesto infer protein function or simultaneously process multiple genomes. To this end, we have developed amanagement and annotation system of genomic data (MAGUS – http://magus.gforge.inria.fr/).

YAGA (Yeast Genome Annotation Automatic) [CN16, CI71] is a pipelined process performing automaticannotation through the implementationof a ab initio predictor and a combiner. YAGA has been successfullyused on genomes of bacteria of the genus Oenococcus [RI36]. Comparative genome and transcriptomeanalysis of these bacteria revealed the existence of common and stem-specific gene repertoires for the stressresponse in relation to adaptation to the ecological niche (wine, cider) [CI33]. The prediction of pseudogenes

2.4. MABIOVIS 61

improves quality annotation bacterial genomes. Other ad hoc approaches have been attempted to studythe plasticity of interesting genomes [CI29, CN3]. Tsvetok (for “Scaling out data and calculations”) is aprototype application based on a NoSQL schema and implementing the MapReduce paradigm[SI7, SI14, II7]to reach scalability when performing comparative genomics computations.

The identification of protein families is commonly accomplished using classification/clustering algorithms,a longstanding research issue in our team. Because NGS produce much larger amounts of data, these ap-proaches must be revisited [CI83]. We proposed extended and more scalable version of algorithms separatingorthologs from paralogs [RI76]. In the context of a clade of bacterial genomes, we analyzed the impact ofad hoc substitution matrices taking into account the compositional bias of these genomes with the aimof improving the prediction of peer relationships [RI55]. To understand the organization of contemporarygenomes, one solution is to reconstruct ancestral states that lead to modern living organisms. We proposeda new method to identify common markers for evolutionarily distant species [RI50]. We applied the com-parative maps and reconstructed a new method for the reconstruction of ancestral architectures based onadjacencies between calculated markers and genomic distances between genomes [RI51]. These algorithmshave enabled the ancestral reconstruction for yeast clade Hemiascomycetes [RI81].

Another aspect of our work is the development of algorithmic methods for analyzing biological structureswith a special focus on RNA data. The molecular function of these biological entities closely relate to theirspatial conformations, thus requiring to analyze both their nucleotide sequence and the inter-nucleotidelinkages called secondary structure. Chaining techniques on trees inspired from the BLAST and FASTAmethods have been designed to address this problem, leading to an optimal chaining algorithm [CI5, RI1](as part of a collaboration with C. Chauve from SFU, Canada). Another example result in this area is theintroduction of filtering strategies for fast searching of noncoding RNA applied to genome annotation [CI28](as part of L. Bourgeade’s PhD). The team has also been a key player in the development of a benchmarkapproach for RNA comparison algorithms (ANR Brasero project, see http://brasero.labri.fr) [RI3].

ModelingThe BioRica framework orchestrates our efforts and results to analyze and study biological processes

by complex systems based on hierarchical modeling of cell behavior [CN1]. We furthermore build hybridapproaches combining multiple formalisms to cover different aspects of cell behavior (available from dedicateddatabases). Our approach has been validated by modeling two systems: the kinetics of fermentation of wine[CI12] and the decision of cell differentiation in the adipocyte and osteocyte path [RI7]. Each system containsseveral models that are under the control of “switches” using coefficients [CN1, RI8]. These theoreticaldevelopments have enabled us to gain international visibility and thus be involved in the development ofinternational standards regarding the reproducibility of in silico simulations of biological [RI86] systems.

We proposed the first global metabolic model of the oleaginous yeast Yarrowia lipolytica (annotated by theGénolevures consortium) by applying our software PATHTASTIC. These results are now part of Biomodelsdatabase [RI56, SI10]. This model results from the extrapolation of the network of Saccharomyces cerevisiae(remote reference) thanks to the exploitation of in silico methods including conservation of orthologousenzymes and the "mapping" of reactions according to the compartments. The model was iteratively refinedby the expertise of biologists combined to analytical predictions of “Flux Balance Analysis”. We also proposedan applied approach based on "flows", combining a simplified model of stochastic Petri nets to a combinatorialoptimization heuristic [RI44]; this study provided a use case for the Systrip tool developed in collaborationwith members of EVADoM [CI38]. Because metabolic networks can be complex and large (several thousandsof biochemical reactions), we developed a model providing a high level view of the network from which detailscan be accessed on demand [RI89].

Another type of biological network is at the center of a fruitful collaboration with the theme EVADoM:regulatory networks involving non-coding RNAs. We proposed an innovative approach to analyse thesenetworks based on RNAV (rna Navigator), a visual analysis software we developed for these networks modeledas graphs of interactions between RNA [CI39]. Computing distances between trees, or being able to build a“consensus” or “average” tree, is fundamental when comparing biological structures (RNA’s, plants) encodedas trees [RI64] [RI47]. Algorithms on sequences and trees have been successfully applied to musical sequences(see the section on the SIMBALS project for more details).


Visual Exploration and Analysis of Massive data – EVADoMOver the period 2009-2014, the EVADoM theme has worked on three main lines of research: data mining,graph drawing and visual interactive exploration of data.

Data MiningData mining can be viewed as an upstream process for visual data analysis. This process consists in a

combination of data transformation, pattern detection and/or numerical measure computation from whichvisual encodings and interaction supporting visual exploration are specified. Exploiting functional depen-dencies to pre-process data, e.g. losslessly reducing the size of data cubes relying on partial materializationas in [CI32, RI6], improves performances. The design of data structures and algorithms that either guaranteefast response time or optimal memory usage is of primary concern.

We also proposed a method for modeling the changes that can be made on a database in order to automatethe construction of data sets facilitating their analysis [RI62]. In [CI52] we worked on techniques for semi-automatic processing of data to interactively explore different relational representations. In [CI9, CHI2], wepresented a method to extract frequent temporal sequence intervals using a sliding time window relaxingthe temporal constraint. In [CI36], we proposed a parallel algorithm for computing borders, widely studiedin the literature because they are found in many applications such as maximal frequent sets or minimalfunctional dependencies.

Another aspect of our research focuses on the development and evaluation of graph decomposition meth-ods. In [CI1], we have defined a method to create a partition of the edges based on the measurement ofcoreness and detect subgraphs invariants for this measure. In [CI91], we have implemented a new metricto limit bias in evaluating the quality of clusters. The literature surveys quality measures for graph de-composition based on inter and intra-communities edge density. Many algorithms are defined from such aquality measure and attempt at finding an optimal decomposition maximizing internal edge density whileminimizing intra-community densities. We proposed a generalization of a quality measure called MQ [RI9]extending quality measurement to graph hierarchies, together with optimization algorithms for hierarchicaldecompositions of graph [CN20]. We also proposed a measure capturing group cohesion in networks basedboth on the intensity and homogeneity of interactions [CI79, CI80]. This work earned Benjamin Renoust theJury Special Mention PhD award (Université de Bordeaux) for his PhD thesis. Finally, we have establishedmethods of generating graphs having certain features such as small-world graphs, scale-free graphs or graphscontaining specific community structures [RI73].

Graph DrawingDrawing graphs consists in emebedding the vertices of a graph in a geometrical space (a 2D Euclidean

space is commonly used in information visualization). We have investigated this area from three differentangles: aggregating edges into bundles to improve readability, visual exploration of a graph driven form ahierarchy of clusters; aggregating nodes into overlapping clusters. We have contributed an innovative edgebundling method based on a discretization of space capturing available 2D tiles of varying size and re-routingedges along shortest paths in this grid-like structure [RI53]. Driving visual navigation from a hierarchicaldecomposition of a graph is a problem we have been closely looking at [RI10, CI8, RI5].

We have developed approaches and algorithms capable of automatically draw a graph as a Euler diagram(a generalization of a Venn diagram) given a set of overlapping clusters [CI84, RI80]. This is of particularinterest in systems biology. The technique is based on the use of the theory of planar graphs and an extensionof a constrained graph drawing algorithm [RI79]. We also proposed a new method to draw metabolic networks[RI54] based on the detection of special topological structures. User evaluations were conducted to evaluatethe effectiveness of various visual representations of dynamic graphs [CI10, RI6]. The results show thatthumbnail based visualizations are often preferable to alernative representations.

Interactive ExplorationWhen designing a visualization system, often starting from user tasks and available data, one must decide

of a proper visual representation coupled with task-relevant interactions. We have investigated the use ofGPU’s to improve interactivity when exploring sophisticated graph drawing for large graphs (typically usingcurves for edges) [RI54, CI43, CI63].

We also tackled the difficult problem of visualizing dynamic graphs, where either changes affect topologyor attributes associated with vertices and edges. We have implemented a system to explore regulatorynetworks whose topology varies with the application of rewrite rules [RI67]. We are also interested in data

2.4. MABIOVIS 63

from metabolomics under fixed topology networks in [CI38]. Finally we proposed a visualization systemfor the detection of targets in regulatory networks of RNA molecules in [CI39]. In this case, dynamicitycomes from users interactively modifying the topology, as well as attribute changes. In [CI9] we conductedan evaluation that shows the advantages and disadvantages of the use of exploration based on multi-scaleapproaches. In [CI82, CI95], we proposed a method of exploring the results of a search query on the internet.

2.4.3 Scientific production


Peer-reviewed journals 92 1Chapters in contributed volumes 10 2Editors of contributed volumes 5 2Invited conference talks 9 2Conferences with published proceedings 96 24Conferences without published proceedings 16 5Other publications 17 7Patents 1Licensed software 2Free software 2Completed PhDs 22Completed habilitations 2

2.4.4 Visibility and attractivity

Editorial and organisational activities


Steering committee 2Program committee 15 12Chair of program committee 1 1Organizing committee (conferences, seminaries, schools...) 7 4Journal editorial board 6 3Research animation 3

Service as expert or evaluator


Membership in expert committee 2 25Individual expert (reviewer) 3Membership in selection board 15Membership in prize jury 3Reviewing of PhD or habilitation 5 14Membership of PhD/habilitation committee 13


Scientific collaborationsScientific collaborations

international nationalProjects 4 22Joint publications 18 9Other collaborations 2Research visitors 3Research visits 10 2

2.4.5 Involvement with social, economic and cultural actorsCollaborations with the industry


Industrial contracts 36Contributions to standards 3

2.5. PROGRAMMING, NETWORKS AND SYSTEMS (PROGRESS) 65

2.5 Programming, Networks and Systems (Progress)

2.5.1 Members

PR MCF CR DR TotalJanuary 1, 2009 - - - - -June 30, 2014 6 8 0 0 14

PhDs defended: 18On-going PhDs: 17Post-doctoral fellowships: 131 monthsStaff (on 2014/06/30): AHMEDToufik (PR, leader of theme Comet), BLANC Xavier (PR), BROMBERGDavid (MCF, leader of theme SE), CASTANET Richard (PR emeritus), CASTEIGTS Arnaud (MCF,deputy group leader), CHAUMETTE Serge (PR, leader of theme Muse), DELORD Xavier (MCF),FALLERI Jean-Remy (MCF), KRIEF Francine (PR), MAGONI Damien (PR), MORANDAT Floreal (MCF),NEGRU Daniel (MCF HDR), RÉVEILLÈRE Laurent (MCF HDR, group leader), RUBI Franck (MCF)All members of our group have a lot of teaching duties and almost all of them fulfill various administrativeresponsibilities at the level of LaBRI, the University of Bordeaux, and IPB Enseirb-Matmeca.Hired Postdocs (2009/01/01-2014/06/30): MERCADAL Julien (2011-2012), AIT CHELLOUCHE So-raya (2012), RAJI Amine (2012-2013), CHEN Yiping (2010-2013), CASSAGNES Cyril (2013-2014), LAVALJannik (2011-2012), OUOBA Jonathan (2013), PALYART Marc (2013), MBAYE Maïssa (2010-2011)PhD students (on 2014/06/30): ANAPLIOTIS Petros, AUTEFAGE Vincent, BARJON Matthieu,BINDEL Sébastien, BRAIKWilliam, CHARPENTIER Alan, DAOUDAAhmat Mahamat, DE ROCHEFORTXavier, DEMIGHA Walid, FOUCAULT Matthieu, MSHALI Haider Hasan, NEGGAZ Mohammed Yessin,OUATTARA Dramane, PERES Martin, QUACH Minh Thao, SOLANKI Jigar, TEYTON Cédric

2.5.2 Scientific reportThe Progress (Programming, Networks and Systems) research group was created in 2012 as the result of therestructuring of the LSR research group. This evolution has been initiated by the head of the LaBRI whodecided to recruit one professor and one associate professor in Software Engineering to reinforce this researchfield. That led to the creation of the SE theme in 2010, and further to the recruitment of another associateprofessor in 2012. At the same period, to address the issue raised by the retirement of the single professorworking in the area of modeling and testing of communicating systems, the Mtsc theme that was part ofthe LSR group has been ended. The two other associate professor members of this theme then moved to theFM research group in November 2011. Further, the Phoenix theme moved to the Satanas research group toenhance the synergy between members of the theme and members of the Satanas group. To sum up, amongthe four themes (Comet, Muse, Phoenix, Mtsc) that made up the LSR group, two of them (Comet andMuse) are part of the Progress group in addition to the newly created SE theme. Research conducted inthe group targets future networked media environments, mobile communicating devices, Internet applicationevolution, and distributed application development. In the remainder of this section, we present for eachtheme its challenges and main achievements during the evaluation period.

Theme Comet : COntext-aware ManagEment and neTworkingThe demand for high-speed networking, driven mainly by the rapid expansion of the Internet and thehigh demand of new multimedia services, has been growing at an exponential rate during the last decade.Next generation networks and services will be highly challenging involving multi-sourced, highly interactiveand distributed resources which are accessed by a large number of users having different preferences andcapabilities across a multitude of heterogeneous access networks. In this context, the support of new value-added services using traditional solutions of pre-provisioning sufficient network resources and computationalpower everywhere is no longer economically viable given the huge capacities required.


The Comet theme aims to propose an optimization and control of future networked media environmentsby dynamic mobilization of network and user resources where it is needed and by enabling applicationsto adapt themselves and the content they are conveying to available network resources, as well as theheterogeneity of access.

The main challenges and achievements are the following.

Optimization and control of content delivery over IP networks. The distribution of the contentfrom a given source to a large and dynamic group of participants is a major challenge. This includes mediaadaptation, quality monitoring, mobility aspects and control of overlay applications to make the best use ofthe capabilities of the underlying networks and the capacities provided by participing end users. We havebeen working on these challenges to provide effective mechanisms for large scale content delivery by tacklingproblems of service discovery, scheduling, and smoothing, but also effective content adaptation to meetthe abilities of the underlying networks and user requirement. Some of these challenges have been tackledas part of the European projects ALICANTE (LaBRI was the coordinator) and ENVISION. We obtainedresults on architectures, protocols, algorithms and mechanisms that optimize delivery of delay-sensitivecontent for home networking, extended-home, and for large scale overlay network [RI33, CHI8, RI34, CHI6,RI42, RI11, CHI5, RI39]. In this context, we proposed a solution to overcome the problems of addressingand routing limitations as well as the tradeoff between communication mobility and security [RI55]. Wedefined an architecture supporting mobile secure networks which implements network virtualization tools[CI22, CI154, CI8] to provide facilities for simulating or implementing different network protocols.

Enabling QoS for challenged networks. Challenged networks present major constraints such as wirelessconstraints, mobility constraints, energy and computational constraints. Most of the envisioned solutionsfor enabling quality of services require global network knowledge whereas conventional expectations fromlink or path characteristics no longer hold compared to conventional networks. In this context, we have de-fined a QoS enabled routing protocol suitable for challenged multihop wireless networks [RI43, RI41, RI53].Furthermore, in the ANR DIAFORUS research project, we developed a framework for in-network reasoningand cooperation in challenged networks. The collaborative detection of spatio-temporally correlated eventsthat we proposed has drastically lowered power consumption by both reducing and localizing communication[CI135]. Moreover, node cooperation combined with adaptive security mechanisms helped achieve overallenergy saving [CI134]. In this context, our contributions were to enable autonomic networking capabilitiesto reduce the cost and the complexity of managing challenged network infrastructures. We proposed (1)self-organization of intelligent systems capable of acquiring and processing information locally, making deci-sions and acting on their environment, (2) capture, aggregation and decentralized processing of information,(3) mobility management taking into account specific constraints. Furthermore, we conduted research andobtained significant results on three specific autonomic network architectures (1) Telecommunications net-works for self-healing [CI103], self-optimizing [CI44, RI10, SI4], and self-protecting[CN5], (2) wireless sensornetworks for self-organizing and self-adaptation (ANR DIAFORUS) and (3) cognitive radio networks (ANRLICORNE) for self-optimizing [RI46].

Theme Muse: Mobility, Ubiquity, SecurityThe aim of the Muse theme is to make it possible, simple and as far as possible efficient, to use andmanage the computing or functional pieces of equipment that are connected to a wireless network. Thisrequires the provision of tools, environments and validated middleware (offering a high level of abstractionwhile allowing a relatively fine grain control of the underlying layers) as well as actual applications. Ofcourse such applications rely on underlying validated algorithms. This research activity was initially focusedon connected coarse grain distributed systems (clusters, grids, etc.) and was based on distributed objecttechnologies. The target of the work has evolved in a natural way to mobile communicating systems, whichare also distributed by nature, but which bring unique challenges.

The activities of Muse rely on the following skills: distributed technologies and associated models;security in a distributed framework (PKIs, smart cards, etc.); mobility related technologies and associatedmodels; distributed algorithms and local computation dynamic graphs; swarming, drones (aerial, ground,surface, underwater, etc.).


The goal of these activities is to facilitate the use of mobile communicating devices by offering developmentmethodologies, tools, and effective secured and formally validated applications, that meet users, programmersand administrators expectations. The applications must therefore be specifically designed to operate in amobile environment and the associated middleware should offer them adequate mechanisms. The problemsof mobility, ubiquity, heterogeneity and safety are major scientific issues, and barriers to the effective use ofthe new opportunities offered by mobile systems. It should also be noted that degraded mode of operation(message and node loss) is the nominal mode of operation in the systems that we consider.


Dynamic networks, distributed algorithms and local computation. The networks that we areaddressing are composed of mobile pieces of equipment that communicate with each other using wirelesstechnologies. The fact that these pieces of equipment can move, appear or disappear from the network at anytime raises the problem of the dynamicity of the underlying graph. While so far the major part of the resultsthat can be found in the literature assume static graphs (or graphs that stabilize to a static configuration, orthat are periodically static) we believe really dynamic graphs need to be specifically addressed. To achievethis goal we extended the existing approaches based on graph relabelings so as to take into account thedynamic environments in which we are interested. In this context, significant results were achieved in termsof modeling and characterization of algorithms and mobile applications [CI55]. This work on algorithms isbeing carried out in relationship with the Combinatorics research group (see for instance [CI4]). One of ourmost significant result is a contribution to a classification of dynamic graphs (that keeps on being extendedby Muse and other research groups). This classification is used to decide on possibility/impossibility results[CI55] depending on the shape of the graph over time. A number of algorithms have also been developedthat take into account the dynamicity of the graph [CI56].

Securing mobile systems. Security is a major issue of dynamic networks because of unsecure boundaries,the lack of central authority to manage identities, and the ease of attack from both the inside and theoutside of the network. Our work on security builds our expertise in the field of smart cards [CHI1], security[CHI1, CHI4] and on a close relationship with the Formal Methods group [SI2]. We made significant progresson trust management in dynamic (unscheduled) mobile networks: based on this expertise we developed anapproach in which each mobile device is equipped with a smart card (see for instance [CI129]). The cardsprovide security services that are used in the higher level layers by the mobile devices. This work partlytook place in the CARUS ans Smart Urban Spaces projects described below.

Applications/demonstrators and tools for fleets of mobile communicating devices. Real worldimplementations are a key topic of our resarch work: it both makes it possible to validate our results andraises new issues. Therefore, we have deployed a number of platforms based on communicating mobiledevices (phones, PDAs and PCs) equipped with Wi-Fi, Bluetooth or NFC. We have extended these resultsto the original field of fleets of UAVs, an area that has been little studied in France and in Europe. Thisbegan within the framework of a project called SYMM that has been labeled by the Aerospace Valley WorldCompetitiveness Cluster. The interaction of the dynamic evolution of the system imposed by the algorithms(designed to achieve a specific mission) with the flight plans of the UAVs has been a major topic of ourwork. We have developed a number of demonstrators, the most significant being the CARUS project[CI80].CARUS (Configurable Autonomous Reconfigurable Uav Swarm) is a project of the LaBRI that was developedwith Thales, Fly-n-Sense, Région Aquitaine and Bordeaux TechnoWest. The goal of the project was to havea swarm of UAVs surveilling an area in a totally autonomous manner. The application is self adaptive andresilient to message and UAV loss. We made many flights at the Souges Military Camp, close to Bordeaux.Another significant result is the creation of the NFC-Interactive startup, that is born from our work in theSmart Urban Spaces European Project [CI132, CI130] (this project received the Best Exploitation awardamong all ITEA2 projects in 2013).

Theme SE: Software EngineeringThe goal of the SE theme is to tame software development by raising the level of abstraction beyondprogramming, overcoming the chaotic nature of software evolution, and mastering the many dimensions ofmodern distributed applications. More particularly, the first key objective to focus on Internet application


evolution. Internet applications belong to a complex ecosystem made of various resources that constantlyevolve on a day-to-day basis. Inherently classical software development becomes inefficient, and worst,may involve a drastically increase of maintenance costs. Proposing significant breakthrough solutions toaddress these challenges is one of the key challenge of the theme. The second key objective is to easethe building of applications and services for heterogeneous interconnected distributed systems. In fact, anincreasing number of different kinds of resources, including everyday objects, are interconnected to eachother. However, interconnected resources may come from various application domains such as aerospace,aviation, telecommunications, agriculture, health-care, automotive, mobile computing, home automation,smart space, smart energy, etc., making their seamless interactions impossible. Providing promising andsuccessful solutions to overcome such bottleneck is another key challenge of the theme.


Internet Application Evolution. From a Software Engineering point of view, Internet is a large ecosystemof different kinds of resources that continuously and independently evolve, which irremediably impacts on themaintenance of all the applications that use them. As a consequence, mastering the evolution of any givenInternet application requires to comply with the evolution of all the resources it uses, with the main objectiveto react to, and/or to anticipate on their changes that have an impact on it. The two major challenges thathave to be overcome to tackle the evolution of Internet applications are therefore: (1) the scale of the Internet,and (2) the granularity of its changes. Indeed, Internet contains a huge set of resources where a little changein one of them can have a major impact on many applications. As a consequence, supporting the evolution ofInternet applications requires to perform analyses on lots of heterogeneous resources. Further, such analysishave to be fined grained to be able to measure adequately the impact of at least one change.

In this context, the SE theme tackles the overmentioned challenges by targeting mainly Open SourceSoftware (OSS) applications. One of the key advantage of OSS is that their Software artifacts are fullyavailable thanks to Version Control Systems (VCS) allowing deep analysis on their history. As a result, theSE theme is able to perform analyses on such artifacts to identify syntactical patterns of evolution, and tomeasure their impact. To that extent, the SE theme has designed Harmony, a framework that supports thedefinition and the execution of Software artifact analyses on the Internet. Harmony provides an abstractmodel that unifies both source code and evolution information on top of which complex analyses can beeasily deployed [AI9]. Furthermore, Harmony provides support for statistical methods, such as sampling,that are used to analyze small but representative sample of Internet applications, with the objective to scaleup, and to obtain significant results [SI7]. Our approach has been successfully used to measure the impactof the evolution of software libraries used by Internet applications [CI148, AI13] and to measure to impactof team organization in large OSS projects [AI10, AI14].

Distributed Application Development. Interoperability is a key challenge as an increase number of het-erogeneous devices of our daily life have to seamlessly interact with each other. However, enabling this stronginteraction is challenging due to both the extreme diversity of devices and the various competing networkedcommunication protocols that have been frequently introduced to support specific domain requirements.Further, it requires an intimate knowledge of the relevant protocols and a substantial understanding of lowlevel system and network programming, which can be a challenge for many programmers. To successfullyreduce the level of expertise required to build efficient, robust, distributed and interoperable applications,the SE theme has provided key tools relying on the design of domain-specific languages and program anal-yses [CI49, CI142, CI97, CI51, CI50, CI97]. In particular, we address interoperability issues through theuse of gateways that translate back and forth messages among heterogeneous protocols. According to thecontext, we provide different kind of gateways that are built following a generative programming approach.In fact, we have designed a domain specific language to describe the gateway behavior, and a compiler thatchecks essential correctness properties and produces code that is plugged into a runtime [RI7]. Further toease the development of runtimes that need to closely interact with the operating system, the SE theme hasprovided an approach to automatically construct a debugging interface for the Linux kernel enabling to easeinteractions with the kernel, to debug in an easy way code related to device driver, file system or networkprotocol [CI37].


2.5.3 Scientific productionOur research activities have a broad spectrum and are attested by numerous publications in the best in-ternational journals and conferences, such as: Software: Practice and Experience, Journal of AutomatedSoftware Engineering, Transactions on Software Engineering, IEEE Journal on Selected Areas in Commu-nications, Journal of Network and Computer Applications, IEEE Transactions on Computers, InternationalConference on Automated Software Engineering, International Middleware Conference, International Confer-ence on Distributed Computing Systems, IEEE International Conference on Communications, InternationalColloquium on Structural Information and Communication Complexity, Symposium on Principles of Dis-tributed Computing, International Parallel and Distributed Processing Symposium, International Conferenceon Theoretical Computer Science.

In the reference period, group members have published more than 50 papers in refereed internationaljournals and more than 150 papers in refereed international conferences with proceedings. We present belowfive publications illustrating the wide wide range of interests of the group.

Selected publications

1. L. Burgy, L. Réveillère, J. L. Lawall, and G. Muller. Zebu: A Language-Based Approach for NetworkProtocol Message Processing. IEEE Transactions on Software Engineering , 37(4), pp. 575-591, 2011

This paper addresses the issues of correctness and efficiency of network protocol message processingcode using a parser-generator-based approach. For this, we present a domain-specific language, Zebu,for describing HTTP-like text-based protocol message formats and related processing constraints.

2. J.-R. Falleri, X. Blanc, R. Bendraou, M. Aurélio Almeida da Silva, and C. Teyton. Incremental incon-sistency detection with low memory overhead, Software: Practice and Experience, 44(5), pp. 621-641,2014

This paper addresses the issue of the detection of inconsistencies within software artifacts. It proposesan incremental approach that requires only a limited set of memory.

3. A. Casteigts, P. Flocchini, B. Mans, and N. Santoro. Measuring Temporal Lags in Delay-TolerantNetworks. IEEE Transactions on Computers, 63(2), pp. 397-410, 2014

This paper introduces a generic distributed tool to measure temporal distances in a highly dynamicnetwork. Using it as an abstraction, several unsolved problems are shown to become easy to solve,such as building fastest (i.e. minimal duration) or foremost (i.e. earliest arrival) broadcast trees inperiodic networks whose connectivity never exist at a given time, but still holds over time and space(e.g. satellite networks).

4. S. Medjiah, T. Ahmed, and R. Boutaba. Avoiding Quality Bottlenecks in P2P Adaptive Streaming -IEEE Journal on Selected Areas in Communications, 32(4), pp. 734–745, 2014

This paper proposes a solution for adaptive SVC streaming over P2P networks which aims to avoidthe issue of received quality bottleneck. This solution depends on overlay formation strategy to allowboth optimized throughput and high peer contribution.

5. M. Grafl, C. Timmerer, H. Hellwagner, G. Gardikis, G. Xilouris, D. Renzi, S. Battista, E. Borcoci,and D. Negru. Scalable Media Coding enabling Content-Aware Networking. IEEE MultiMedia. 20(2),pp. 30-41, 2013

This paper presents a proposal built on the exploitation of scalable media coding technologies within acontent-aware networking (CAN) environment for Future Media Internet. Four representative use casesfor media delivery (unicast, multicast, peer-to-peer, and adaptive HTTP streaming) are consideredand CAN challenges are reviewed upon them, more specifically flow processing, caching/buffering, andQoS/QoE management.



Peer-reviewed journals 55 2Chapters in contributed volumes 13 2Editors of contributed volumes 2 3Invited conference talks 4Conferences with published proceedings 156 8Conferences without published proceedings 11 3Other publications 14 5Patents 1Licensed software 5Free software 11Completed PhDs (without cotutelle) 18Completed cotutelle PhDs 1Completed habilitations 2

2.5.4 Visibility and attractivityAlthough recently created, our group has a recognized national and international visibility. Indeed, membersof the group have served as reviewer of PhD or habilitation 85 times (national) and 9 times (international).In addition, members of the group have also been invited as member of PhD or habilitation committees 45times. Furthermore, members of the group have received several distinctions including :

1. Best paper award at the International Conference on Automated Software Engineering, September2012 (T. Bissyandé & L. Réveillère)

2. Best PhD award from Armée de l’air, 2013 (R. Laplace)

Finally, the attractivity of the group is attested by the appointment of 1 full professor (X. Blanc 2010)and 3 associate professors (Falleri 2010, A. Casteigts 2012, F. Morandat 2012).

Program committees, steering committees, organizing committeesMembers of the group are actively involved in more than 100 program committees (national and international)which is very large for such a small group. Furthermore, one of our members (Laurent Réveillère) has beennominated general chair of two top ranked international conferences (Middleware 2014 and EuroSys 2015)that will be located in Bordeaux.


Steering committee 3 1Program committee 94 14Chair of program committee 3Organizing committee (conferences, seminaries, schools...) 9 6Journal editorial board 8Research animation 6

Service as expert or evaluatorMembers of the group are frequently asked for making expertise for different institutions. In addition, itshould be noticed that members of the group are highly involved in PhD and habilitation committees.



Chair of expert committee 1Membership in expert committee 2 22Individual expert (reviewer) 6Chair of selection board 3Membership in selection board 31Membership in prize jury 2Reviewing of PhD or habilitation 9 85Membership of PhD/habilitation committee 45

Scientific collaborationsOur group is involved in a large number of national and international cooperations as attested by the followingnumbers. One of our members (Daniel Négru) was the main coordinator of the ALICANTE European FP7ICT project (17 partners).


Projects 3 15Joint publications 26 22Other collaborations 1Research visitors 5 11Research visits 5 12

2.5.5 Involvement with social, economic and cultural actorsOne of the strength of our group is its interaction with social, economic and cultural actors. Further, theresearch fields covered by the group clearly meet the priority of companies and governmental agencies. Thisis attested by the fact that many CIFRE PhD thesis are supervised in our team. Moreover, one start-up hasbeen created and another one is currently incubating.

Collaborations with the industryThe following numbers show that our team has several contracts with industrial partners. The table alsoshows that our group has many interactions with industrial partners without any formal contract.


Industrial contracts 5Contributions to professional journals and overview publications 1Reports for decision makers 3Collaborations outside of universities 12Start-ups 1

General audience actionsMembers of our group fairly participate to general audience actions. Our actions target professionals as wellas students.


Scientific popularization, dissemination of scientific culture 6

2.6. SATANAS 73

2.6 Supports and Algorithms for High Performance NumericalApplications (SATANAS)

2.6.1 Members


PhDs defended: 29On-going PhDs: 30

Staff (on 2014/06/30): AGULLO Emanuel (CR), AUMAGE Olivier (CR), BARTHOU Denis (PR),CONSEL Charles (PR, Head of PHOENIX Inria project), COULAUD Olivier (DR), COUNILH Marie-Christine (MCF), DANEY David (CR), DENIS Alexandre (CR), ESNARD Aurélien (MCF), FAVERGEMathieu (MCF), GIRAUD Luc (DR, Head of HIEPACS Inria project), GOGLIN Brice (CR HDR),GUERMOUCHE Abdou (MCF), JEANNOT Emmanuel (DR), MERCIER Guillaume (MCF), NAMYSTRaymond (PR, Head of SATANAS Team, Head of RUNTIME Inria project), PELLEGRINIFrançois (PR), RAMET Pierre (MCF, Deputy Head of SATANAS Team), ROMAN Jean (PR onInria secondment), THIBAULT Samuel (MCF), WACRENIER Pierre-André (MCF)

Hired Postdocs (2009/01/01-2014/06/30):

PhD students (on 2014/06/30): ALZAIX Benjamin, ARRAS Paul-Antoine, BAGHDADI Soufiane,BERTRAN Benjamin, BLANCHARD Raphaël, BRAMAS Béranger, CAPRA Antoine, CASADEI Astrid,CIEREN Emmanuel, COUTEYEN-CARPAYE Jean-Marie, DUDOUIT Yohann, ETCHEVERRY Arnaud,GENET Damien, HAINE Christopher, HUGO Andra-Ecaterina, KABACMilan, KUMAR Suraj, LACOSTEXavier, LI Pei, MOUSTAFA Salli, NAKOV Stojce, PREDARI Maria, ROSSIGNON Corentin, ROZARFabien, SABAÏLA Bruno, SAILLARD Emmanuelle, SERGENTMarc, TESSIER François, VAN DERWALTPaul, ZOUNON Mawussi

2.6.2 Scientific reportThe SATANAS team is mostly focusing on HPC, with a strong background in numerical methods, parallelalgorithms, mesh partitionning techniques and runtime system design. During the last two years, the teamscope has been extended toward the design of principles, domain specific languages and software techniquesfor orchestration of networked entities. The team currently gathers researchers belonging to four LaBRIthemes which actually correspond to Inria projects:

BACCHUS (F. Pellegrini - M. Ricchiuto) Parallel tools for Numerical Algorithms and Resolution ofessentially Hyperbolic problems

HIEPACS (J. Roman - L. Giraud) High-End Parallel Algorithms for Challenging Numerical Simula-tions

PHOENIX (C. Consel) A Multi-Disciplinary Approach to Orchestrating Networked Entities

RUNTIME (R. Namyst) Efficient runtime systems for parallel architectures

In the remaining of this section, we discuss the most significant scientific advances we have achievedduring the evaluation period.


Toward Runtime Systems for Exascale machines

During the 2009-2014 period, we took the opportunity to investigate a significant number of new researchtopics thanks to the arrival of new, senior researchers and to the anticipation of new challenges 5. Mostnotably, we have anticipated the massive coming of accelerators in HPC and have started a highly visibleresearch effort about programming heterogeneous hardware featuring multicore processors coupled with ac-celerators (e.g. Nvidia GPU, Intel MIC). To tackle the complexity of such hybrid architectures, we havedesigned StarPU, a task-based runtime system which handles both task scheduling and memory man-agement [CI16, RI9], thus relieving the application programmer from both concerns. StarPU pioneeredresearch on runtime systems for hybrid machines in 2008. By automatically calibrating performance modelsfor the tasks [CI14], it uses state-of-the-art scheduling algorithms to optimize execution, as well as dataplacement [CI13]. We have demonstrated that complex applications can exhibit higher efficiency over hy-brid machines than over any of the machine’s homogeneous subset of processing units [RI9]. StarPU wasalso extended using MPI communications to exploit clusters [CI12], and proved to be able to exploit newaccelerators such as the Intel SCC and Intel MIC coprocessors. More recently, we extended the scope ofthis work to the OpenCL ecosystem [CI113]. Research around StarPU was done as a ground for numerouscollaborations (EU and ANR projects), and has inspired several research efforts about dynamic scheduling onhybrid systems. This work has gained international visibility: the StarPU runtime system is widely knownand cited in scientific papers (paper [RI9] has more than 430 citations). In particular, it is most notablyused by the state-of-the-art MAGMA dense linear algebra library (developped by Jack Dongarra’s group atICL, UTK, USA), by the SkePU skeleton library (developped by Christoph Kessler’s group at LinköpingUniversity [CI47, CI25, CI82], Sweden), and by the XcalableMP parallel language [CI102, CI9] (MitsuhisaSato and Taisuke Boku, University of Tsukuba, Japan). It is also used by Airbus (H-Matrix computations)and CEA/DAM (Dense linear solvers).

Denis Barthou, who joined our group in 2009, is a specialist of code analysis and optimization tech-niques. He brought new research areas in the domain of code optimization and compilation. He reinforced theexisting collaboration with Urbana-Champaign on high-level expression for task programming and broughta collaboration with the Exascale Computing Laboratory on performance analysis of multithreaded codes.Understanding why performance reaches some given level and how to improve it is essential in high perfor-mance computing. We have developped, within a collaboration with Intel, a method for exploring trade-offsbetween energy and performance for large manycores as the Intel SCC [CI106]. More generally, we havedevelopped inside the tool MAQAO [CI11, CI45] new analyses for performance tuning. These analysesuse static and dynamic approaches – combining a performance model with measurements – and provideunique feed-backs to optimize multi-threaded applications. We have also developped new code generationtechniques for homogeneous or heterogeneous architectures, taking advantage of their architectural features[CI75, CI21]. The originality of the approach taken is to start from programs with a richer semantics (Stencilcode patterns and a domain-specific language for equational and algorithmic description for physics prob-lems) and propagate this information to compiler/runtime levels. For stencil code pattern, the methodunifies memory constraints for both multicore and GPU architectures, taking into account vectorization andalignment issues in task generation. The same approach, for different architecture, generates codes thatcompares or outperforms existing hand-tuned codes. We designed for Lattice QCD simulations a high levellanguage for physicists. This input expression, very close to the mathematical expression of the physics,enables physicists to explore easily algorithmic variants that fit best the architecture. The code generatorproduces parallel code for multicores. This approach is very different from related works, where codes aregenerally hand-tuned and do not offer the same versality.

Emmanuel Jeannot, who arrived in 2009 with a strong background in algorithmics and scheduling,brought new research areas in the domain of thread and process placement, especially for message-passingbased applications in the context of hierarchical multiprocessor systems. We showed that a proper MPIprocesses binding policy within NUMA nodes induces significant impact for parallel application performanceWe proposed an automatic placement scheme that gathers information about the application communicationpatterns during a preliminary run so as to place processes according to their communication affinities and

5We did coordinate the writing of the document devoted to “Challenges for Runtime European Systems” in the context ofthe European Exascale Software Initiative (EESI). We did also contribute to the writing of the Strategic Research Agenda ofthe ETP4HPC prospective UE action.

http://icl.cs.utk.edu/magma/

http://www.ida.liu.se/~chrke/skepu/

http://www.xcalablemp.org

2.6. SATANAS 75

to the hardware characteristics such as shared caches or NUMA nodes. We developed a specific algorithm(called TreeMatch) for matching the processes to the resources in order to reduce the communicationcost of the application [CI79, RI31]. We have also developed an accelerated version of the algorithm forenabling on-the-fly decision. This version have been ported into the Charm++ framework as a dynamicload-balancer [CI80]. In order to allow the users to utilize our work in a portable way, we enhanced someroutines of the MPI standard. Instead of modifying the binding of the MPI processes onto the physicalcores on the underlying architecture, we chose to create a new communicator for which the logical topologyorganization is optimized for the hardware. It brought interesting performance improvements for some classof MPI applications [CI95]. The problem of process placement, which can be reduced to a NP-hard graphpartitionning problem, can be dealt with several famous applications like Scotch or ParMETIS. To evaluatethese solution with TreeMatch, we ran several benchmarks using NAS Parellel Benchmarks and a realCFD application. On the one hand we studied the quality of processes permutation (which will impact theexecution time) and on the other hand the computation time of the permutation.

A Paradigm-oriented design languageTo raise the level of abstraction beyond programming, the key approaches are model-driven engineering andarchitecture description languages. These approaches are often general-purpose in nature, do not properlycover the stages of the development life-cycle, and poorly leverage the programming support and developmentenvironment of mainstream programming languages.

We introduce a paradigm-oriented development approach that revolves around a conceptual frameworkconcretized by a design language [CI46]. A design description is used to generate high-level programmingand testing support, to perform a range of verifications, and to abstract over underlying technologies.

Our approach is illustrated with the Sense-Compute-Control (SCC) paradigm, where a SCC softwaresystem gathers information about an environment via sensors (whether hardware or software) and issuesorders to impact the environment via actuators. The SCC paradigm has a wide spectrum of applicability; wehave used it successfully in the domains of home/building automation, multimedia, avionics and networking.

Our proposed SCC paradigm is concretized with a design language, named DiaSpec. It consists of twolanguage layers: (1) one layer is for declaring a software system at the functional level, decomposing itinto context and control components, and defining how these components are connected to each other; (2)another layer is for declaring the sensors and actuators to be used by the SCC software system.

The decomposition of a SCC software system into components and their interaction is a key sourceof information for implementation guidance, programming support, and static verification. We introducedinteraction contracts as a refinement of DiaSpec to express the interactions that are allowed between com-ponents and their constraints in terms of data and control flow [CI21].

Going beyond a contemplative strategy, we developed a compiler for DiaSpec based on generative pro-gramming [CI42]. Given a DiaSpec description, this compiler generates a dedicated programming frameworkthat provides high-level support to implement a design and factors out underlying technologies. Because thegenerated programming frameworks are in Java, rich integrated development environments and vast APIscan be used to implement a design.

A tool-based development methodology.We introduce a tool-based methodology for developing real-size pervasive computing applications [RI18]. Ourmethodology provides support throughout the development life-cycle of a pervasive computing application:design, implementation, simulation, and execution.

First, the taxonomy of the target area and the design descriptions are written in the DiaSpec language.Then, the DiaSpec compiler processes these descriptions and generates a dedicated programming framework.This framework raises the abstraction level by providing the programmer with high-level operations for entitydiscovery and component interactions. A pervasive computing simulator, DiaSim, is used to simulate theenvironment. Finally, the DiaSpec compiler back-end enables to deploy an application using a specificdistributed systems technology.

The evaluation of our methodology has demonstrated its benefits along three criteria: expressiveness,usability, and productivity. Furthermore, our methodology and our tool suite have been successfully applied


to the development of realistic pervasive computing applications in a wide spectrum of areas [CI43, CI44,RI13].

High-End Parallel Algorithms for Challenging Numerical SimulationOver the last few decades, there have been innumerable science, engineering and societal breakthroughs en-abled by the development of high performance computing applications, algorithms and architectures. Thesepowerful tools have provided researchers with the ability to computationally find efficient solutions for someof the most challenging scientific questions and problems in medicine and biology, climatology, nanotechnol-ogy, energy and environment. For application codes to sustain petaflops and more in the next few years,hundreds of thousands of processor cores or more will be needed, regardless of processor technology. Cur-rently, only a few HPC simulation codes easily scale to this regime and major code development efforts arecritical to achieve the potential of these new systems. Scaling to a petaflop and more will involve improv-ing physical models, mathematical modeling, super scalable algorithms that will require paying particularattention to acquisition, management and visualization of huge amounts of scientific data.

In this context, our purpose has been to perform efficiently frontier simulations arising from challengingresearch and industrial that are likely to be multiscale and coupled applications. The solution of thesechallenging problems require a multidisciplinary approach involving applied mathematics, computationaland computer sciences. In applied mathematics, it essentially involves advanced numerical schemes. Incomputational science, it involves massively parallel computing and the design of highly scalable algorithmsand codes to be executed on emerging hierarchical many-core platforms. Through this approach, HiePACS(which is a follow-up of the previous Inria project-team ScAlApplix) intends to contribute to all steps that gofrom the design of new high-performance more scalable, robust and more accurate numerical schemes to theoptimized implementations of the associated algorithms and codes on very high performance supercomputers.This research is conduced on close collaboration in particular with European and US initiatives or projectssuch as PRACE (Partnership for Advanced Computing in Europe), EESI-2 (European Exascale SoftwareInitiative 2) and likely in the framework of H2020 European collaborative projects.

The methodological part of HIEPACS covers several topics. First, we have address several generic studiesconcerning massively parallel computing, the design of high-end performance algorithms and software to beexecuted on future extreme scale platforms. For this, we have developped a strong collaboration with theRUNTIME group in order to use high performance runtimes to achieve very efficient implementations onnowadays hybrid architectures. Next, several research in scalable parallel linear algebra techniques havebeen addressed, ranging from dense direct, sparse direct, iterative and hybrid approaches for large linearsystems. It’s a major contribution which led to the design and the implementation of a complete stack of highperformance software (MORSE, MUMPS, PaStiX, HIPS, MaPHyS) that have been at the center of manyacademic (national and international) and industrial collaborations (AIRBUS, CEA, EDF, TOTAL). In thesame way, we have developped deep research activitries for N-body interaction computations based on efficientparallel fast multipole methods (ScalFMM software) and finally, we have adressed more recently researchrelated to the algorithmic challenges for complex code couplings in multiscale simulations (in collaborationwith CERFACS).

At the application level, we have focused on one major multiscale application that is in material physics(dislocation dynamics in collaboration with CEA Saclay). We contributed to all steps of the design of anefficient parallel simulation tool. More precisely, we have contributed to the modeling and our advancednumerical schemes will help in the design of and efficient software implementation (OPTIDIS) for very largeparallel multiscale simulations. As said above, the robustness and efficiency of our algorithmic research inlinear algebra have been validated through industrial and academic collaborations with different partnersinvolved in various application fields. Finally, we are also involved in a few collaborative industrial intia-tives in various application domains in a co-design like framework (ITER Challenge with CEA Cadarache,ARIANE 6 project with AIRBUS Defence & Space).

Parallel methods and tools for graph and mesh handlingData structures such as graphs and meshes are ubiquitous in the field of scientific computing. Meshes areabstract representations of physical media within which some phenomenon is to be numerically simulated.

2.6. SATANAS 77

Graphs have many uses, such as the representation of the pattern of sparse matrices, or of the communicationpatterns in scientific applications. Exascale-class software based on these abstractions require tools that areable to handle graphs and meshes comprising more than a billion vertices and/or elements6. The aim ofa small group of people within the BACCHUS team (which is a follow-up of the previous Inria project-team ScAlApplix) is to provide methods and toolboxes for scientific application writers, that will allowthem to handle graphs and unstructured meshes of exascale class, focusing on two key issues: parallel graphpartitioning and mapping (e.g. for process-processor placement on hierarchical, heterogeneous architectures)and parallel remeshing. The design and operations of these toolboxes is validated by the members of theBACCHUS team who design numerical schemes and solvers.

Regarding parallel graph partitioning and mapping, we first focused on the development of parallel graphpartitioning methods that preserve partition quality for increasing numbers of processors, which previouspartitioners did not provided. These methods were backed by software development which allowed ourreference implementation software, Scotch, to partition efficiently graphs over more than 2 billion edges onseveral thousand processors, as the first full 64-bit implementation of a general purpose graph partitioner.This turnpoint led us to define a new roadmap that specifically targets exascale. Indeed, the advent ofmassively parallel, non uniform machines imposes to re-think the design of the software to be executed onthem. Since, in the context of dynamic repartitioning, parallel mapping software will have to run on theirtarget architectures, parallel mapping and remapping algorithms suitable for efficient execution on suchheterogeneous architectures have to be investigated, that tackle simultaneously the challenges of scalability,heterogeneity and asynchronicity, away from the flat model of global, collective communication primitives.We devised scalable parallel algorithms for remapping graphs [CN4], whose implementation into production-grade software is under way. The evaluation of our techniques for real-scale scientific applications is thecenter of a collaboration with the Charm++ group of UIUC, within the Joint Laboratory for PetascaleComputing (JLPC) between INRIA and UIUC.

Regarding parallel unstructured mesh management, our work focused on remeshing and repartitioning.Both are mandatory features for dynamically evolving, mesh-based simulations, so as to capture more accu-rately the properties of the phenomenon in areas of interest, and to adapt processor workload consequently.We developed a general framework for parallel remeshing on distributed-memory machines, based on theconcurrent application of existing sequential remeshing tools to centralized representations of parts of themeshes [SI42]. Last December, our prototype software, PaMPA, which provides many features for writingnumerical schemes using an abstract representation of a distributed mesh and of its numerical data, has beenable to remesh a coarse mesh of 27 millions of tetraedra up to a fine mesh comprising more than 600 millionsof tetraedra, in 34 minutes, on 240 processors, using the MMD3D sequential remesher also developed withinBACHUS. PaMPA is already used as the data structure manager for two solvers being developed at INRIA:Plato and and AeroSol [RI35]. Recently, INRIA decided to start a consortium to foster the industrial transferof the PaMPA library.

2.6.3 Scientific production

The quality of our research activities is attested by their publication in top level international conferences (e.g.SC, IPDPS, HiPC) and journals (e.g. Siam SISC, JCP, IEEE TPDS, JPDC, CCPE), and by the productionof registered software libraries which are used worldwide for academic research and which have also beentransferred to the industry (e.g. parallel linear algebra solvers, graph partitioners, runtime systems). We areparticularly proud of some highly cited papers (e.g. [RI9] is already cited more than 465 times, which makesit one of the top ten most cited papers in the Computing Systems domain7) which highlight our pionneerresearches.

6In that respect, we were in charge of the “partitioning methods” section of the report produced within the “EuropeanExascale Software Initiative” (EESI-1) FP7 project, and we contributed to the “mesh management” section of its followupEESI-2.

7Source: Google Scholar



Peer-reviewed journals 38 4Contributed volumes 7 2Chapters in contributed volumes 12 2Invited conference talks 3Conferences with published proceedings 119 10Conferences without published proceedings 52 7Other publications 48 14Licensed software 16Free software 13Completed PhDs (without cotutelle) 29Completed cotutelle PhDs 1 5Completed habilitations 2

2.6.4 Visibility and attractivityOur team is involved in many actions at the international level regarding the organization of events andthe evaluation of scientific activities (e.g. organization of EuroPar’2011, DSL’2011 and PreCond’2011, par-ticipation to a high number of top conference program and expertise committees) and at the national level(expert missions, juries, etc.).

Editorial and organizational activities


Steering committee 2Program committee 146 8Chair of program committee 9Organizing committee (conferences, seminaries, schools...) 6Chair of organizing committee 4Journal editorial board 2

Service as expert or evaluator


Chair of expert committee 2Membership in expert committee 15Individual expert (reviewer) 29Membership in selection board 28Membership in prize jury 1Reviewing of PhD or habilitation 7 41Membership of PhD/habilitation committee 30

Scientific collaborationsSatanas is involved in several fruitful scientific collaborations at the international level, mainly in the frame-work of Inria associate teams with USA (ANL, LBNL, Stanford, UTK-ICL) and Canada (Montréal) andwithin European projects.

2.6. SATANAS 79


Projects 20 21Joint publications 19 13Other collaborations 4Research visitors 7Research visits 2

2.6.5 Involvement with social, economic and cultural actorsCollaborations with the industryThe team has a strong impact in terms of industrial transfer, due to a sustained software developmentactivity. This has led to an significant contractual activity, resulting in several external fundings for PhDstudents.


Industrial contracts 15Reports for decision makers 2Contributions to standards 1Start-ups 1

General audience actionsSome of the research activities of team members are strongly connected to social issues, e.g. the supportof autistic children in primary school classrooms. Many team members are also involved in conferences andevents that highlight the social implications of their works, e.g. Fête de la Science. Moreover, some teammembers have participated in hearings held by parliamentary commissions, and have been appointed to sitin national bodies focusing on social issues of information sciences.


Scientific popularization, dissemination of scientific culture 5Publications for large audience 2

2.7. TRANSVERSAL PROJECT RHOBAN: THE ROBOT WORKSHOP 81

2.7 Transversal Project RHOBAN: The Robot Workshop

2.7.1 MembersPR MCF DR CR Total

June 1st, 2009 0 2 0 1 3June 30, 2014 0 2 0 1 3


Staff (on 2014/06/30): Olivier Ly (MDC), Hugo Gimbert (CR), Aymeric Vincent (MDC)

PhD students (on 2014/06/30): Quentin Rouxel, Grégoire Passault (CIFRE).

2.7.2 Scientific reportRhoban project is a transversal project of the LaBRI. It is focused on robotics, and especially humanoid andautonomous robotics.

Legged robotics and locomotion.For forty years until today, biped locomotion remains an open question. Even if it is the most elementary

ability of human being, it remains a major issue when designing a humanoid robot. No humanoid robotcan walk like human being, with the same robustness, reliability or efficiency. We are interested in thisquestion at different levels, from mechanics to control. Concerning mechanical architecture, we investigatein particular passive and semi-passive motor primitives, relying a part of control on mechanics, followingidea of morphological computation.

We have designed several humanoid robots : at first RhoBan, then AcroBan (in collaboration withFlowers Inria Team), SigmaBan, or also MicroBan.

We investigate the role of morphology and compliance in legged locomotion and balance keeping. Com-pliance is the ability of the robot to enforce soft motions like animals instead of stiff ones. Let us mentionthat studying biped locomotion applies to therapeutics of Musculoskeletal diseases in a natural way.

Compliance is also interesting when thinking about human / robot interaction. Seeing that a robot isessentially a computer provided with a sensori-motor system, physical interaction with human is natural andcharacteristic. Compliance is necessary to allow the user to engage physical interaction with the robot.

More generally, Physical interaction is a way to think about the more general concept of CoBots (Collab-orative Robots) whose applications flourish at the moment, industrial applications, but also entertainmentapplications. We work on industrial applications of this concept in collaboration with SAFRAN/Heraklesand ENSC.

International Expo 2012Our team has been selected to organise and expose the major robot room of the french pavillion at

International Exposition 2012 in YEOSU in Korea, with about 8 millions visitors.In a practical way, let us note that we exposed 13 robots (anthropomorphic arms and humanoid robots)

focused on physical interactions, between the robots themselves but also with people, every day, during 3months.

Autonomous robotics and Precision FarmingRhoban project has developed several autonomous robots, including humanoid robots (sigmaban) but

also precision farming autonomous robot (based on a backhoe). These project allowed us to develop acomplete and modular control environment, including mechatronic control, but also geolocalisation based inparticular on GNSS techniques.

We indeed developed a complete low-cost geolocalisation system based on simple frequency differentialGPS, with centimetric precision.

Today, our technology is actually deployed in agriculture industry (Vine), alowing precision tasks. It hasbeen primed in Vinitech 2012.

We are developing precision weeding machine, in collaboration with Razol company. The point is toreplace the usage of chemistry by precision robotics in weeding operations.


Rhoban gave rise to a startup company in collaboration with Bordeaux University and CNRS in orderto transfer these technologies to agriculture industry, this company already created 2 employments.

Robocup.Our activities on autonomous robotics and humanoid robotics converge in the design on a full autonomous

robot: Sigmaban. We participate with this platform to the robotics world-cup: The RoboCup, which includesrobotic research teams all around the world. The challenge is to develop a complete team of fully autonomoushumanoid robot playing soccer.

The challenge is at each level of robotics: mechanics, mechatronics, control, architecture, motor primi-tives. We develop a team of 3 humanoid robots playing soccer: the Rhoban Football Club.

This year (2014) has been our third participation and we have achieved the quater of finals, putting usin the 8 best teams of the world on about 40 teams (in humanoid kid-size league).

2.8. TRANSVERSAL PROJECT SIMBALS 83

2.8 Transversal Project Simbals

2.8.1 Members

PR MCF CR DR TotalJanuary 1, 2009 3June 30, 2014 4

Staff (on 2014/06/30): Pierre HANNA (MdC), Julien ALLALI (MdC), Matthias ROBINE (MdC), PascalFERRARO (MdC)

2.8.2 Scientific reportThe number of digital music documents available on the Internet is highly increasing. However the onlyavailable tools are based on browsing from text queries (name of songs, performers). New methods forretrieving or classifying musical pieces have to be proposed. One of the key issues is then the developmentof algorithms for estimating the musical similarity between audio data.

Measuring similarity between sequences is a well-known problem in computer science having applicationsin many fields such as computational biology or text processing. However, musical sequences are characterizedby specific properties and then imply to take into account areas such as sound perception and music theoryin the development of efficient and accurate algorithms.

Since 2006, a cross-domain project in the LaBRI proposes to develop systems for estimating musicalsimilarity by considering several properties, mainly from music theory, like for example melody, harmony,key, rhythm, etc. This multi-disciplinary research team gathers both Image and Sound and MaBioVis teamstaff members.

Modeling Musical InformationConsidering audio databases has required the development of new algorithms for analyzing musical prop-

erties from audio signals, taking into account harmony, rhythm or timbre. This was the first main part ofthe researches leaded by the Simbals project.

Methods for analyzing tonal information, like key or chord progression, have been studied during the PhDof Thomas Rocher. These researches rely on the estimation of accurate features describing tonal contextand on a system based on musical rules, and propose an analysis based on dynamic programming [CI222].Moreover, a first tree model of tonal information has been proposed. Rhythm and timbre are two other mainmusical characteristics. In order to be able to analyze and compare these informations, specific features,similar to chromas for tonal information, have been proposed [CI156].

Another part of researches concern the analysis of musical structure. These studies have been leaded byBenjamin Martin during his PhD. Most of western music are made of repeated patterns. Thus, a musicalpiece can be described as repetitions of structures (for example verses, chorus), repetitions of chords orrepetitions of notes. The occurrences are not exact: for example a chorus may be transposed, accelerated,etc. We have proposed an algorithm to extract repeated factors in a musical piece [CI47]. This has led to anautomatic system for estimating the musical structure of any piece [CI188]. This system has been evaluatedduring international evaluation MIREX as one of the most efficient existng system.

Application to large databasesFor a few years, browsing large databases has become a classical operation. Based on dynamic program-

ming, local alignment methods investigate all the possible mappings between two musical pieces and returnthe optimal local alignment as result [RI1]. This exhaustive analysis is very costly from a computationalpoint of view. The exponential growth of databases makes the use of exact alignment algorithms impossible.Alternatives have been proposed in Bioinformatics, by applying heuristics or by developing faster implemen-tations. One major part of the reasearches leaded in the Simbals project concerns the adaptation of theexisting method for measuring similarity between musicla pieces to huge databases.

The first approach relies on the indexing of musical pieces [CI48]. It has already been applied with successin Bioinformatics and leads to tools like BLAST, one of the most used and efficient tools of the Bioinformatics


community. The main idea of this approach consists in indexing pieces of the database in order to be ableto quickly retrieve exact occurrences of fragments of the query. Once the potential candidates have beenidentified, an alignment algorithm allows refining results [CI46].

In parallel, the quality of the results obtained by applying exact comparison algorithms lead us to developnew faster implementation. Indeed, we have proposed to consider the huge computation power of graphiccards available in public domain in order to develop high performance applications for Query-by-Hummingor plagiarism detection for example [CI27].

Applications and Industrial transferApplications from our cross-domain project are numerous. We thus aim at developing musical content-

based search engines. Musical pieces could then be retrieved from a symbolic query, based on the similaritywith respect of the melody, the harmony, the rhythm, the timbre or the structure. Current works on structureinference or detection of repetitions in musical pieces may lead to propose automatic systems to summarizemusical pieces.

Another kind of applications concerns the development of musical video games and of some new teachingtools for musicians. The quality of the feedback, the rightness of the evaluation of a musical performance isan essential aspect for a gamer or a student. We aim at applying our similarity systems, using the advantagesof the alignment algorithms, to compare the musical performances to models issued from either a score, theperformance of an expert, or the same performer in the past. A global score may be computed, and thedifferences could also be precisely located. Adapting the feedback to the technical level of the performer(correctness of the notes for a beginner, of the tuning for a more advanced student) may improve the efficiencyof the teaching process in identifying the main technical lacks [CI183, CI182].

All these potential applications lead us to develop a start-up Simbals for facilitating the technologytransfer between the results obtained in our cross-domain project and the industry. Such transfer impliesthe registration of patents [BI1].

The cross-domain project Simbals has allowed the developpement of original methods for estimatingmusic similarity. Research activities will now continue in both Image and Sound and MaBioVis teams.

2.9. TRANSVERSAL PROJECT VISIDIA 85

2.9 Transversal Project Visidia

2.9.1 Members

PR MCF DR CR TotalJune 1st, 2009 2 1 0 0 3June 30th, 2014 2 2 0 0 4

PhDs defended: 5On-going PhDs: 1

Staff (on 2014/06/30): CASTERAN Pierre (MCF), METIVIER Yves (PR), MOSBAH Mohamed (PR),ZEMMARI Akka (MCF).

PhD students (on 2014/06/30): OULED ABDALLAH Nesrine.

2.9.2 Scientific reportThe Visidia Project is a transversal project which aims at developing a unified environment for modeling,proving, analyzing and implementing distributed algorithms. This project involves many areas, includingdesign and analysis of algorithms, formal proofs, graph algorithms, etc. Therefore, members of this projectbelong to distinct teams, mainly Formal Methods and Combinatorics and Algorithms. The ambition ofthis project is to build an integrated framework, together with tools and methods, that makes it easy todesign, prove and program distributed algorithms. In the following, we mainly concentrate on the model oflocal computations that has been extensively studied and implemented. Moreover, we introduced a novelapproach that combines formal proofs and local computations that defines formal semantics for distributedalgorithms.

Local computationsDistributed algorithms are difficult to design and to study, and even to represent, mainly when nodes

communicating only with their neighbours must participate to achieve a global goal (election of a leaderin a network, distributed computation of a spanning tree). We introduced an original formalism in thisdomain, namely graph rewritings. In this formalism, a distributed system is represented by a labeled graph;the nodes represent the processors and the edges represent the links between them. The labels are used toencode the internal states of processors and/or channels. A rule in such a calculus is defined by a smallcontext graph together with two labeling configurations to this context – one to describe the local state beforerule application, and one to specify the local state after rule application. The transformation is strictly local;there are no long-distance side-effects.

A rewriting system is defined by a finite set of such rules. In our work, we consider asynchronous ruleapplication: there is no global clock available, and two conflict-free applications of rewriting rules may occursimultaneously, provided they do not attempt to modify the same local context in the host graph. Thus, thebehaviour of the network is defined by its initial labeling and the rule base of the associated local rewritingcalculus. The types of these rules define classes of local computations.

We have also developed a software tool called Visidia which allows to visualize the execution of a dis-tributed algorithm by using a friendly GUI. A catalog of distributed algorithms, including election of aleader or the computation of a spanning tree, is already implemented and the execution of each algorithmcan be directly visualized. To help users developing new algorithms, a set of Java primitives can be used toimplement and test such algorithms. This tool is used to teach distributed algorithms, and is mainly usefullfor projects of master students.

Formal proofs of distributed algorithmsProving the correctness of distributed algorithms may be hard and tedious if it is performed by hand.

For complex distributed algorithms, it is even very difficult to be convinced of such a correctness. To haveintuition about the proof, visualization of the executions of algorithms provided by the Visidia platform canbe of great help, but confidence can be strengthened by certifying the correctness of these algorithms usingformal methods. Relying on local computations, our work aims at the development of not only particularproofs for isolated algorithms but also the development of generic properties for classes of algorithms. Wehave started this work by exploring the use of refinement proofs. A catalog of proved distributed algorithms


has been developed on the RODIN platform together with a tool that generates automatically a Visidiacode from a B-event specification of an algorithm. The benefit of such a generation is to implement and tovisualize in the Visidia environment distributed algorithms that are formally correct. The high level encodingof distributed algorithms by graph relabeling systems makes it easy the integration of mathematical proofsinto distributed algorithms. A general proof schema for proving distributed algorithms encoded by localcomputations was built. On the other hand, we formalized the semantics of local computations with theproof assistant Coq. The aim of this work is to construct a specific proof environment for local computationsthat can be used by non specialists. We have already obtained new results for the certain classes of algorithms.In addition to a complete proof of an election algorithm in a tree with initial knowledge of degrees, we provedthat there exists no election algorithm in a non decorated tree.

In this framework, we could also formalize and certify a generic transformation that automatically broad-casts local detection of global termination to all nodes, and explore some sufficient conditions for makingthe composition of local computation systems meaningful.

Transformations and compositions of algorithms are much more complex to define and prove in a dis-tributed framework than for sequential programs. In 2013, we started to define in Coq a new syntax andoperational semantics for local computation systems with the following features:

- LC systems are represented in a parametric higher-order abstract syntax (PHOAS), the constructionsof which allow to define transformations and compositions of algorithms as functions written in Coq’s spec-ification language.

- An operational semantics for these systems is written in a purely functional style. The step by stepexecution of the algorithms is driven by distributed probabilistic local election algorithms.

- A few generic transformations and compositions, as well as various examples are gieven in the library,called Loco.

The integration of the formal proofs built in our previous models, as well as the work on analysis ofdistributed random algorithms is the next step of the evolution of this library. An extraction of provenalgorithms towards Visidia will be also an important task.

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