Cellular Automata vs. Agent-Based Models

[Dawn Trembath]

I'm trying to understand the distinction between Cellular Automata &
Agent-Based Models.  The information on Craig Reynold's webpage
http://www.red.com/cwr/ibm.html was very helpful, with his basic
distinction being that in a CA model you look at the world as a dense and
uniform dissection of space, whereas in an agent-based design your world is
based on specific individuals distributed within the space.  I'm now trying
to understand the practical issue of why one would choose to use a CA
representation, vs an ABM approach.  

On one hand, there's a very staightforward answer - you use the approach
that best fits your problem.  But, since it appears that there is a fair
amount of overlap between the two, things are still a bit muddy for me.  In
a CA model, if you allow your automata to be mobile, and to act
non-homogeneously through the application of If-Then rules, I can think of
examples where I would have a hard time deciding between the two approaches.

Maybe some direct questions would clear this up for me the fastest.  Why
was Swarm implemented using an Agent-Based approach as opposed to a very
unrestricted CA approach?  If anyone is modeling a system that could be
represented using either design, why did you choose the one you did?  Does
a commonly used tool exist for building CA models?  (StarLogo?  In the CA
studies I've seen, people seem to write their own code.)  Finally, if
anyone knows of a reference where the two approaches are compared, I'd
appreciate hearing about it.  

Thanks very much for any insight you can provide.




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