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The Basics of Bio Science Simulation System1

Santosa2

ABSTRACT

In the universe, the system is complex. To learn it, we need system model,

assumption, and system border. However, in general it can be stated that three patterns of

systems feedback, i. e. (a) system with positive feedback, (b) system with negative

feedback, and (c) system with positive and negative feedback. A simulation model that

applies positive feedback pattern will produce exponential graph, where the level will

increase into the higher accretion level. A simulation model that applies negative

feedback pattern will produce asymptotic graph, where the level value will increase (or

decrease) with accretion level (or reduction) that increase (or decrease) until it is very

close to a certain value. For example, temperature control system in plenum of dryer

machine that using thermostat. The example of simulation model that applies positive

and negative pattern is the growth of rat population, after the corrector of rat population

density in system is added. For dynamic simulation system, there is a computer program

with Visual Basic 6.0 software.

Keywords: Simulation, Dynamic System, Visual Basic 6.0.

INTRODUCTION

A system approach is a way to shows the complex nature phenomenon into a

mathematical model, a way to watches the characteristic of system if the compiler parts

experienced values change.

A dynamic system is an approach that uses feedback, where the current level

determines the level in the future. In dynamic system approach, there are 3 important

aspects, i. e. (1) causal loop relationship, (2) feedback relationship, (3) the current border

system (Djojomartono (1989) in Santosa (2009)).

1Paper Presented at International Seminar on Food & Agricultural Sciences 2010 in Bukittinggi, 16 18

February 20102Lecturer in Faculty of Agriculture Technology, Andalas University Padang

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DYNAMIC SIMULATION

CAUSAL LOOP CYCLE

With the base of causal loop in a system, primary feedback can be identified

without differ the form of intercorrector. The chart that shows causal loop relationship

has roles:

a. In model development, causal loop chart can be used as the base of illustration of

the causal loop relationship that happens.

b. Causal loop chart is function to simpler the illustration of a model (Santosa, 2009)

System border is needed to determined clearly. The component or the element

outside is unnoticed. If the corrector outside border enters inside border, the input

corrector stated as exogenous input, and it comes from a component called

source. For the corrector that comes from the system through border system will

collected in a component called sink (Santosa, 2009)

SYSTEM MODELLING

The defining of the structure of system into causal loop chart form cannot

illustrate in detail of event and the kinds of system inside the system. So, in illustrating

the structure of a system clearly, we need a flowchart to explain the structure that we

want.

The symbols in dynamic system modeling are (Robert, 1983; Santosa, 2009):

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THE DYNAMIC SIMULATION SYSTEM WITH POSITIVE FEEDBACK

PATTERN

Example: Dynamic System of Human Population Development

Causal loop relationship in a system of human population development is shown by Figure 1.

Figure 1. The Causal Loop Relationship in a System of Human Population Development

In loop 1. (a) If the natality increased, the population increased too, (b) if the population

increased, the natality increased too, and (c) the polarity of cyclical relationship above is positive.

In loop 2. (a) If the population increased, the mortality increased too, (b) if the mortality

increased, the population decreased, (c) the polarity of cyclical relationship above is negative.

In general, the population can be increased or decreased, depends on the number of

natality and mortality. If the natality bigger than mortality, so in general the population will

increased, and it follows exponential pattern.

The flowchart of dynamic system of human population development is shown by Figure

2.

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Figure 2. The Flowchart of Dynamic System of Human Population Development

THE DYNAMIC SIMULATION SYSTEM WITH NEGATIVE FEEDBACK

PATTERN

Example: the simulation of plenum temperature controller system with thermostat.

The example of system that applies negative feedback pattern is plenum

temperature controller system in dryer machine of agriculture product using thermostat

(Santosa, 2005b), where the flowchart of dynamic system is shown by Figure 3.

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Figure 3. The Flowchart of Plenum Temperature Controller System with Thermostat

From the simulation result table we can see that the temperature of plenum

increased paralleled with extra time, but the level of temperature acceleration is

decreased. So, that is the negative feedback pattern, produces asymptotic patterns.

THE DYNAMIC SIMULATION SYSTEM WITH BOTH POSITIVE AND

NEGATIVE FEEDBACK PATTERNS

Example: The simulation of rat population development by adding the rat population

density factor.

The example of system that applies both positive and negative feedback patterns

is rat population development (Santosa, 2005a; Santosa, 2005b). The following flowchart

of system dynamic is shown by Figure 4.

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Figure 4. The Flowchart of Rat Population Development by Adding the Rat PopulationDensity Factor

From the simulation it is clearly at beginning step, rat population increase with the

bigger acceleration. But after pass through a certain point, the population increased with

smaller acceleration. So, in general the characteristic of rat population development

pattern is sigmoid.

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CONCLUSIONS:

1. Simulation model that applies positive feedback pattern produces exponential

graph, where the level will increased with bigger acceleration. Example: human

population system, where the natality is bigger than mortality.

2. Simulation model that applies negative feedback pattern produces asymptotic

graph, where the level will increased (or decreased) with smaller acceleration, until it

is very close to a certain value. For example, the plenum temperature controller

system with thermostat.

3. The characteristic of simulation model that applies both positive and negative

patterns is sigmoid. For example, the rat population system after the corrector of rat

population in system is added.

REFERENCE

Roberts, N. 1983. Introduction to Computer Simulation. Lensley College. Addison

Wesley Publishing Company. Massachusetts. California.

Santosa. 2005a. Simulasi Dinamik dengan Dynamo Compiler. Jurnal Teknologi

Pertanian Andalas. Volume 9 No. 1. September 2005. hal. 22-30.

Santosa. 2005b. Aplikasi Visual Basic 6.0 dan Visual Studio.Net 2003 dalam Bidang

Teknik dan Pertanian, ISBN : 979-731-755-2, Penerbit Andi, Edisi I Cetakan I,

Yogyakarta.

Santosa. 2006. Simulasi dan Pemodelan Sistem Pertanian. Ceramah Ilmiah

disampaikan di Fakultas Pertanian UNAND pada Tanggal 5 Oktober 2006.

http://santosa764.wordpress.com [24 Desember 2009]

Santosa. 2009. Ilmu Sistem. Program Studi Teknologi Industri Pertanian. Program

Pascasarjana, Universitas Andalas, Padang.

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