[FRIAM] The art of agent-based modeling

[Jochen Fromm]

One question I meet again and again if I try to
make meaningful agent-based simulations is:
- How do we simulate the core of a problem
  without merely constructing an illustration
  of our own beliefs and assumptions ?
In other words: How detailed should an agent-based 
simulation be ? If the goal is "to capture the principal 
laws behind the exciting variety of new phenomena that become 
apparent when the many units of a complex system interact", as 
Tamas Vicsek says in http://angel.elte.hu/~vicsek/images/complex.pdf
then how do we design models that are complex enough but not too 
complex ?

-If the simulation is too simple and matches your 
 own theoretical ideas, then no matter how good these 
 ideas are it is always easy to criticize that the 
 simulation is either not realistic enough or only 
 constructed to illustrate your own ideas and assumptions. 
-If the simulation is too complex and matches 
 official experimental data, everything takes a 
 lot amount of time (creation, setup and execution of
 the experiment and finally the cumbersome analysis
 of the complex outcomes), and it becomes increasingly 
 difficult to identify the principal laws, because it is 
 easy to get lost in the data or bogged down in details

The "art of agent-based modeling" looks really like an art 
to me, something only mastered by a few scientists (for instance 
Axelrod). Grimm et al. propose 'pattern-oriented modeling',
Macy and Willer say "Keep it simple" and "Test validity".
What do you think is the best solution for this problem ?

Macy and Willer
"From Factors to Actors: Computational Sociology and Agent-Based Modeling"
http://www.casos.cs.cmu.edu/education/phd/classpapers/Macy_Factors_2001.pdf

Grimm et al. 
"Pattern-oriented modeling of agent-based complex systems"
Science Vol. 310. no. 5750 (2005) 987-991
http://www.ufz.de/index.php?de=4976

-J.

-----Original Message-----
From: Michael Agar
Sent: Saturday, August 12, 2006 5:05 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] complexity and society

[...] If you are considering a model, I like Axelrod's way of thinking  
about them. He sees them as "thought experiment labs" for a  
conclusion based on social research. So first of all the social  
research has to be solid to really do it properly. More often than  
not it isn't.

The lab let's you test arguments of the form, if people do things in  
particular ways properties will emerge at the level of society. By  
"test" I mean it lets you see if the conclusion can be "generated,"  
to use Epstein and Axtell's concept, in just the way your social  
research suggests that it can. It's a way of making the argument that  
underlies the conclusion explicit so it can be better evaluated, and  
it allows for exploration of the space of results that the same  
argument produces and alternative spaces given control parameter  
changes. It's a test of plausibility and an exercise in clarity,  
nothing more, nothing less. [...]