Re: simulating large models

[Jason Alexander]

> Does anyone have experience with simulating large models with swarm?
> Is swarm prepared to distributed simulations across several
> processors/machines?
> We're  thinking of large market models which may include hundreds (or 
> even
> thousands) of customers (agents) and we foresee scalability problems.

A model including hundreds or thousands of agents will not, in 
principle, present a problem unless your agents are particularly complex 
or resource hungry.  Swarm easily handles lattice models  where each 
slot in a grid is occupied by an agent and the lattice has dimensions 
200x200 or 300x300 (so you have 40000 or 90000 agents existing at once).

What does become more important with large models are the algorithms you 
use for manipulating the population. Inefficient algorithms which don't 
seem to slow things down in small models can easily become a bottleneck 
in large models. If the agents are of heterogenous types, using the 
standard Swarm messaging methods can also incur a performance hit, 
unless things have changed recently.  One of my lattice models in which 
the agents were heterogenous slowed down by an order of magnitude 
because of some internal changes to Swarm's messaging methods required 
to support the Java interface.  However, I was able to avoid this 
performance hit by using an alternative method of passing messages to 
the agents.

If I remember correctly, Swarm doesn't support distributed models in a 
transparent way.  (That is, you write a model and Swarm distributes the 
computational load across several machines.)

However, I'm always a bit curious as to why one might need to do this, 
aside from the coolness factor. You can get a Linux box with 2 or 4 
high-speed processors and a gig of ram (or more) for reasonable amounts 
nowadays.  With a box like that I would think one would be able to do an 
awful lot, especially if one wrote the model efficiently. (I.e., instead 
of having 24 separate boolean variables, use a single int with bit 
arithmetic.)

Cheers,

Jason

--
J. McKenzie Alexander
Department of Philosophy, Logic and Scientific Method
London School of Economics and Political Science
Houghton Street, London WC2A 2AE


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