Locating and Operationalizing the Analytic Horizon

In the previous post, Miguel explored simpleA.mdl as an introduction to a technique for agent-based modeling based on constructivist identity theory. This model consists of 2500 agents, each with an activated identity and a repertoire of five other subscribed identities. As the model runs, agents are able to activate new identities from within their repertoire, trade identities within their repertoire for other identities present in the landscape and even activate on identities present in the landscape but not present in the agents repertoire at the time. If you watch simpleA.mdl run, you can observe this behavior as agents assess their environment, decide what identities are available to them (as dictated by their identity repertoire and the triggers that determine under what conditions an agent will rotate their activated identity, substitute a new identity for a subscribed identity, or activate a new identity from outside the agents' repertoire), and activate on the optimal identity.

Primoridialism, Instrumentalism, and Constructivism

In our last two examples, agents in the model represented trees and abstract "live" cells.  But it's easy in agent-based modeling to start thinking of your population of agents as people, rather than abstract entities.  A very common way to view the world is that people are agents in a social environment, meaning that they have the agency to change their behavior according to that world.

Self-Organized Criticality

In 1987, a physicist named Per Bak published a paper in which he and others introduce the term "self-organized criticality".  He developed a machine that dropped grains of sand onto a disk, and counted the number of avalanches which occurred.  He found that most of the time, a grain of sand would hit the pile and only slightly adjust the configuration of grains.  Once in a while, a small avalanche would occur, sending sand right off the disk.  But rarely, an avalanche with a size several standard deviations above the mean would knock the pile down to a fraction of its previous size.  They hypothesized that the sand pile was attracted to a critical state, at which point the next grain of sand could cause a near-complete collapse of the pile.  He also found that the distribution of avalanches followed a power law, meaning that the size of an avalanche was inversely proportional to its frequency over time.  Systems that follow a power law also create distributional fractals, since the distribution is self-similar and scale invariant.

PS-I and the Game of Life

Our first step into the PS-I world is to download the program and check it out.  You can download the most recent public version by going to the PS-I Sourceforge site and downloading version 4.0.5 (exe installer).  This installer will by default install the program to your Program Files directory, but you might want to install it into your documents folder or desktop.  The reason for this is that PS-I uses its root folder to look for files, and newer versions of windows do not automatically give writing access to PS-I in the Program Files folder.

Welcome to Beyond the Analytic Horizon!

As the description of this blog makes clear, we would like to start a dialogue about agent-based modeling and its role in the increasingly large body of literature on social science with a non-linear perspective.  Specifically, we would like to explore the use of PS-I, a platform developed by Ian Lustick, professor of Political Science at the University of Pennsylvania, and Vladimir Dergachev, currently working with the LIGO project.  Future posts will be geared toward getting someone started with PS-I, and we will continue to add useful PS-I tips as well as ways to learn more about the subject's we'll be interested in posting about.