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 modelsin the social sciences

2Today’s agenda

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

3Simple sample models

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

4

Example 1: Neighborhood segregation

Move to random location otherwise

Micro-level rules of the game

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

< 1/3

Thomas C. SchellingMicromotives and

Macrobehavior

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

6Example 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

7Example 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

8Example 5: Labour Market

• Agents represent workers in an international labourmarket

• 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)

9Complex 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

11Example 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

12Example 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/

13Example 4: ILUTE

• Integrated Land Use Transportation Modeling from Toronto

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

14ILUTE continued

15ILUTE continued

16Where 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

17Gearing 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)

18Development Environment

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

b++;else

a++;

Java source code

EditorJava

compiler

Integrated Development Environmente.g. IDEA

JVM

Java libs Repast libs