Advanced Game Theory guest lecture
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Transcript of Advanced Game Theory guest lecture
GOALS, REASON, AND DANGEROUS
THINGSAn über-ludological approach to game analysis unabashedly rooted in economic game theory
Advanced Game Theory, Sep 24 2007
JONAS HEIDE [email protected]
“It helps […] to think of a game’s structure as akin to an economy, or
an ecosystem; a complex, interacting system that does not dictate
outcomesbut guides behavior through the
need to achieve a single goal: energy, in the case of ecosystems; money, in the case of economics;
victory, in thecase of a game.”
Costikyan, G. (2002). I Have No Words & I Must Design: Toward a Critical Vocabulary for Games. Paper presented at the
Computer Games and Digital Cultures Conference Proceedings, Tampere.
Game theory is…
“…the formal study of decision-making where several players must make choices that
potentially affect the interests of the other players.”
An analytical framework (and general form of notation)
A design tool
An embattled interdisciplinary current
A promise for the unification of the social sciences
The end of the world
AGENDA
BITS OF BACKGROUNDTHE LOGIC OF GAME THEORY
TOOLS AND CONCEPTS
VIDEO GAME APPLICATIONS
“For that which is common to the greatest number has the least care bestowed upon it. Every one thinks chiefly of his own, hardly at all of the common interest”
“If it was a matter of hunting a deer, everyone well realized that he must remainfaithful to his post; but if a hare happened to pass within reach of one of them, wecannot doubt that he would have gone off in pursuit of it without scruple..."
Jean-Jacques Rousseau
Neumann, J. v., & Morgenstern, O. (1944). Theory of Games and Economic Behaviour.
Strong position in economics, mathematics, evolutionary biology, and computer science. Less strong in anthropology, sociology, game studies.
AGENDA
BITS OF BACKGROUNDTHE LOGIC OF GAME THEORY
TOOLS AND CONCEPTS
VIDEO GAME APPLICATIONS
ECONOMICSA person will make those choices which are likely to maximize his or her satisfaction (utility)
A person does not care about other people’s utility
We don’t know people’s preferences a priori (and we should observe behaviour, rather than simply ask)
GAME THEORYIn many situations one’s best choice depends on the choices of others
Your best choice depends on your belief about the other players’ beliefs about your beliefs about…
Highlights information, perception, and strategy
NIGHT DRIVING
Bob Alice
Alice is driving down a poorly lit road and hears the sound of an oncoming driver. On which side should she drive? Crashing = 0 satisfaction pointsPassing safely = 5 satisfaction points
NIGHT DRIVING
AliceLeft Right
Bob
Left
Bob: 5 points
Alice: 5 points
Bob: 0 pointAlice: 0 points
Right
Bob: 0 points
Alice: 0 point
Bob: 5 pointsAlice: 5 points
Assumes that Bob and Alice have the same preferencesPayoffs represent ranking of outcomesGame theory models social situations as if they were games
AGENDA
BITS OF BACKGROUNDTHE LOGIC OF GAME THEORY
TOOLS AND CONCEPTS
VIDEO GAME APPLICATIONS
MODELLING GAMESStrategic form (choices are
made simultaneuously)
Extended form (can model a game over time, can include bluff etc.)
Current Odysseus: 0 pointsFuture Odysseus: 1 point
Current Odysseus remains free
Current Odysseus has himself tied to mast
Future Odysseus ignores sirens
Future Odysseus succumbs to song
Future Odysseus ignores sirens
Future Odysseus succumbs to song (blocked)
Current Odysseus: 1 pointsFuture Odysseus: 0 point
Current Odysseus: 1 pointFuture Odysseus: 0 points
Current Odysseus: 0 pointFuture Odysseus: 1 points
LET’S PLAYTwo playersEach player chooses either ”Nice” or ”Nasty”Points:
Nice/Nasty: Nice gets 0 points, Nasty gets 5 points
Nice/Nice: Both get 3 points
Nasty/Nasty: Both get 1 point
The most famous of all game theory “games”
The object of thousands of studies
Models a “social dilemma”; a situation where one is tempted to do something which would lead to disaster if everyone made the same choice
Alice
Cooperates Defects
Bob
Cooperates
Bob: 3 points
Alice: 3 points
Bob: 0 points
Alice: 5 points
Defects
Bob: 5 points
Alice: 0 points
Bob: 1 point
Alice: 1 point
PRISONER’S DILEMMA
CHICKEN GAMEAlice
Swerves Does not swerve
BobSwerves
Bob: 2 pointsAlice: 2 points
Bob: 1 pointAlice: 3 points
Does not swerveBob: 3 pointsAlice: 1 point
Bob: 0 pointsAlice: 0 points
First to swerve loses. If no-one swerves, both die.
SUM AND CONFLICTZero-sum games (constant-
sum games): The total outcome is zero (e.g. chess). One players gain is the other player’s loss. Two-player zero-sum games present no incentives for cooperation. With more players, temporary coalitions may form.
Non-zero-sum games: The total outcome is not fixed (e.g. the Prisoner’s Dilemma, tournament soccer). The player relationship depends on the specific outcomes.
INFORMATIONComplete information: All players know everything about the game structure
Perfect information: The full history of the game is known to all players.
The players…… are informed about every change of the
game state
… are not informed about every change of
the game state
… know everything about the game state before the
game starts
Complete and perfect informationE.g. Chess, Checkers,
Parcheesi, Croquet
Complete but imperfect information
(rare)
… do not know everything about the game state
before the game starts
Incomplete but perfect information
E.g. Battleship, Master Mind, Monopoly
Incomplete and imperfect information
E.g. Risk, Mafia, Mah-Jong, Poker
The four information types (traditional games)
STRATEGYA strategy is a complete plan of action for any possible game situation (could be written down in advance and executed by someone else)
Easy to specify in the Prisoner’s Dilemma but very difficult in chess
A strictly dominant strategy is one which yields the highest outcome (for a player) regardless of what the other players do
EQUILIBRIUMStrategic equilibrium refers to the “solution” of a game: A state which a game will tend towards
The Prisoner’s Dilemma has one (unique Nash) equilibrium (defect-defect)
No one player can unilaterally change his strategy for a better outcome: ”I can do no better, given that the other player keeps doing what he is doing.”
AGENDA
BITS OF BACKGROUNDTHE LOGIC OF GAME THEORY
TOOLS AND CONCEPTS
VIDEO GAME APPLICATIONS
“The stories in most video games serve the same purpose as calling the über-checker a ‘king.’ It adds interesting shading to the game but the game at its core is unchanged.” (Koster, 2005: p85)
“…the dimensions of Lara Croft’s body… are irrelevant to me as a player, because a different-looking body would not make me play differently… When I play, I don’t even see her body, but see through it and past it.” (Aarseth, 2004: p48)
PLAYER RELATIONSHIP
Competitive games are constant sum games (the total payoff is fixed). In two-player competitive games, no incentives for cooperation exist at all, while for games with more players, such incentives may occur transitorily
Semi-cooperative games are non-zero sum games which reward team-work over mutual non-cooperation but provide temptations for individuals to act selfishly.
Cooperative games are non-zero sum games which reward players for coordinating their strategies; i.e. they reward team-work and provide no temptation for selfish play.
Cooperative game Alice
Right Left
BobRight
Bob: 1 pointAlice: 1 point
Bob: 0 pointsAlice: 0 points
LeftBob: 0 pointsAlice: 0 points
Bob: 1 pointsAlice: 1 points
Fire Truck (Atari, 1978)
Players’s utility functions are identical (they even have a collective score count).
From the perspective of either, hurting the other player means hurting oneself
Players will cooperate fully
Semi-cooperative game
Wizard
Cooperate Defect
Valkyrie
Cooperate
V: 2 pointsW: 2 point
V: 0 pointsW: 3 points
DefectV: 3 pointsW: 0 points
V: 1 pointsW: 1 points
Gauntlet (Atari, 1982)
Players have an incentive to cooperate but a temptation to defect
Cooperation will be unstable
Competitive game
Alice
Peaceful Aggressive
Bob
Peaceful
Bob: 0,5 point
Alice: 0,5 point
Bob: 0 pointsAlice: 1 points
Aggressive
Bob: 1 pointsAlice: 0 points
Bob: 0,5 points
Alice: 0,5 points
Spacewar (Russel et al, 1962)
Players cannot rely on each other to be peacefulThere will be no cooperation
PLAYER RELATIONSHIP
STRATEGIC DOMINANCE
“A well-designed game shouldn’t contain an option that is never worth using […] A dominated option is worthless. You wasted your time putting it in your game. A dominant option is worse. It means that all the other options are worthless.” (Rollings & Morris, 2004: p62-63)
STRATEGIC DOMINANCE
All video games have dominated strategies and that is unproblematic
In some games the challenge is choosing between alternatives.
In other games the challenge is discovering one’s options or implementing one’s choice.
The former should not have dominant strategies, but the latter should not be ignored.
From a game theory perspective a video game is an incentive structure inside which players maximize their outcome
Game designers assume that players accept the objective game goals
Game theory is an excellent tool for testing such assumptions
Binmore, K. (1991). Fun and Games: A Text on Game Theory. Lexington-Toronto: D.C. Heath.
Smith, J. H. (2006). The games economists play: implications of economic game theory for the study of computer games. Game Studies: The International Journal of Computer Game Research, 6(1).
Smith, J. H. (2006). Plans and Purposes: How Videogame Goals Shape Player Behaviour. Unpublished PhD dissertation, IT University of Copenhagen, Copenhagen.
Smith, J. H. (Forthcoming). Tragedies of the Ludic Commons. Game Studies.
Thanks for your attention
jonassmith.dk [email protected]