There are three kinds of uses of parallelization here that I'd like  

to disambiguate:



0  Parallelizing an experiment within a single machine.



1. Parallelizing a single experiment by spreading it across multiple  

machines that work together.  This  commonly involves one or both of  

the following tasks.



	1.a Distribute the *space* of the world across multiple machines

	    because it's so big in memory

	1.b Distribute the *agents* of the world because their

	    computational cost is too large



2. Using multiple machines to do multiple experiments, one experiment  

per machine.





#0 is trivial.



For #2, shell scripts and rsh do just fine for us; indeed use of PVM/ 

MPI etc., is just way too heavyweight, particularly since Java and  

MPI don't play well together still.  #2 is also very cleanly done on  

grid computing solutions.  If anyone's interested, there's a company  

in my area (Parabon) which negotiates to borrow excess cycles on  

organizations' PCs and then sells this time with a Java-only piece of  

grid computing software.  For a large NASA project they've adapted my  

ECJ code to this system and I'm sure would be interested in tasks you  

might have in MASON.  Give 'em a call (parabon.com).



For #1, I'm very interested in knowing how people are adapting MASON  

(or RePast) to distribute their experiment.  Do you have 1.a as a  

need?  1.b?  How are you going about hacking MASON etc. to do it?



The reason I ask is that one of our grants may push us to look into  

creating a version of MASON which does #1 cleanly.  Note that MASON  

was specifically designed for #2, and indeed *good*, efficient  

architectures are very different between #1 designs and #2 designs.   

So we're going to have to think about what kinds new data structures  

will we need.  Probably at least we'll need a distributed schedule  

sync device, a way for agents to migrate, and several mechanisms for  

distributing space.  It's a lot of overhead.



I'm interested that some have mentioned RePast.  RePast etc. weren't  

designed for #1 *or* #2.  I know people have been hacking  

distribution onto RePast, and am interested in how they overcame the  

issue of the schedule containing single-machine Java events (repaints  

etc.).  It might help inform us when we get to working on this.



Sean