Prof. Lars-Erik CedermanCenter for Comparative and International Studies (CIS)

Seilergraben 49, Room G.2, lcederman@ethz.chNils Weidmann, Room E.3, weidmann@icr.gess.ethz.ch

http://www.icr.ethz.ch/teaching/compmodelsLecture, October 26, 2004

Introduction to Computational Modeling of Social Systems

Examples of agent-based models

in the social sciences

2

Today’s agenda

• Sample runs of simple models• More complex models• Where to find more models• Gearing up

3

Simple sample models

1. Schelling’s segregation model RePast2. Traffic simulation NetLogo3. AIDS NetLogo4. Sugerscape Ascape5. Labour Market Simulation RePast

4

Example 1: Neighborhood segregation

Thomas C. SchellingMicromotives and

Macrobehavior

< 1/3

Micro-level rules of the game

Stay if at least a third of neighbors are “kin”

Move to random location otherwise

5

Example 2: Traffic simulation (NetLogo)

• Model of the movement of cars on a highway

• Each car follows a simple set of rules:– if there’s car close ahead, it slows down– if there’s no car ahead, it speeds up

• The project demonstrates how traffic jams form spontaneously without obstacles

6

Example 3: AIDS (NetLogo)

• Simulate the spread of the human immunodeficiency virus (HIV), via sexual transmission

• Control of the– population's tendency to

practice abstinence– amount of time an average

"couple" in the population will stay together

– population's tendency to use condoms

– population's tendency to get tested for HIV

7

Example 4: Sugarscape (Ascape)

• Series of models introduced by Epstein and Axtell 1996 Growing Artificial Societies MIT Press

• Emergent features:– wealth distributions– social networks– migration– population dynamics– conflict patterns– price formation– credit networks

• Programmed in Ascape

8

Example 5: Labour Market

• Agents represent workers in an international labour market

• Agents’ main goal is to have a job and friends

• Jobs are available according to a country’s economic situation

• If the agent has been unhappy for a certain time period, it moves to another country

(Model developed by Pedro Thomi as SS04 CompModels term project)

9

Complex sample models

1. Anasazi village formation2. Nationalist insurgencies in Geosim3. UrbanSim4. ILUTE

10

Example 1: Anasazi Village Formation

• Gumerman et al. 2002 SFI Working Paper 02-16-067 (among others)

• Reconstruction of settlement patterns and demographics of pueblo Indians in the American Southwest

• The main puzzle pertains to the group’s sudden disappearance

• Based on the Sugarscape model, and thus also programmed in Ascape

11

Example 2: Geosim

• Geopolitical simulation system

• Cederman 2004 “Articulating the Mechanisms of Nationalist Insurgencies”

• Based on RePast

32144421

3##44#2# • National identities

• Cultural map

• State system

• Territorial obstacles

12

Example 3: UrbanSim

• UrbanSim is a simulation model for integrated planning and analysis

• Developed at the Univ. of Washington, Seattle

• Features decision-making by households, businesses, developers and governments

• http://www.urbansim.org/

13

Example 4: ILUTE

• Integrated Land Use Transportation Modeling from Toronto

http://www.civ.utoronto.ca/sect/traeng/ilute/

14

ILUTE continued

15

ILUTE continued

16

Where to find more models: Links

• See “Resources” under class home page• Santa Fe Institute: http://www.santafe.edu/

• Center for the Study of Complex Systems at the University of Michigan: http://www.pscs.umich.edu/

• European web sites on Computer simulation of societies http://www.soc.surrey.ac.uk/research/simsoc/ and “European Social Simulation Association” http://essa.eu.org/

• For the US counterpart, see http://www.dis.anl.gov/naacsos

• Leigh Tesfatsions’s site on computational economics:http://www.econ.iastate.edu/tesfatsi/ace.htm

• See also the Journal of Artificial Societies and Social Simulation: http://jasss.soc.surrey.ac.uk/JASSS.html

17

Gearing up

• Installing the Java 2 SDK• Installing IntelliJ IDEA• Create the main project definition• Create and run a simple test program• Adding the RePast module (and

optionally Ascape and NetLogo) • Setting up Schelling’s segregation

model (depends on RePast)

18

Development Environment

int a = 12;if (a == b) b++;else a++;

Java source code

EditorJava

compiler

Java libs

Integrated Development Environment e.g. IDEA

JVM

Repast libs