Re: Are there theorems for Agent Based Models

[Sven N. Thommesen]

I believe Huberman and Glance had a paper where they investigated just this
difference, and they discovered that doing it in way #2 overturned previous
results achieved with way #1. Their conclusion was that it makes a Big
Difference how you arrange the order of actions.

I'll dig out the reference if you need it.

-Sven

At 03:27 PM 7/12/1999 -0500, you wrote:
>An economist said to me the other day, "where are your theorems? Aren't
>there established results that guide modeling choices?"  I shrugged.
>
>Here is an example of where there is probably a theorem, somewhere,
>somehow.  Consider lots of agents who can observe the behavior of other
>agents within a neighborhood and then adjust their behavior. 
>
>Lately I've noticed you can write this kind of a simulation 2 ways.
>
>1. Assume all agents survey the environment as it was after the last
>time step.  If agents are in time 2, for example, they look around at
>all other agents as they were at the end of time 1.  (Example:Heatbugs
>heat display is updated once per time period, all agents refer to that
>snapshot)  
>
>2. Assume that all agent actions have "instantaneous effects" on each
>other.  If we are in time 2, each agent who observes is able to see all
>agent actions up to that instant.  If in time 2, a long list of agents
>is called upon to act (possibly in random order), each one is aware of
>the actions of the previous agents.  Agents who acted in step 2 before
>are seen and their changes are taken into account.
>
>These 2 approaches yield some initial differences in test models I've
>been working on, but the effects seem to be short term.  
>
>Is there a theorem that says something about the likelihood of
>divergence in observations based on the 2 specifications?
>
>
>
>-- 
>Paul E. Johnson                       email: address@hidden
>Dept. of Political Science            http://lark.cc.ukans.edu/~pauljohn
>University of Kansas                  Office: (785) 864-9086
>Lawrence, Kansas 66045                FAX: (785) 864-5700
>
>
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