Hello all,



We've been using Mason for some simulations now and discovered a

"feature" which can be very annoying.



It seems that the scheduler is using the random generator provided by

the SimState.  Which means that if you have a different amount of

schedulable objects or schedule an object at different intervals this

will influence the randomness of the simulation.



Currently we are using Mason to simulate the behavior of a distributed

application and we have an evaluation algorithm to see if a certain

distribution is ok, or that some servers are overloaded.  If servers are

overloaded an optimisation algorithm kicks in and redistributes the

application.  (in one step).



We run our evaluation function (through a schedulable object)  every 200

steps and in every step a the client behavior is simulated by other

steppables.

The invocation of the evaluation happens by scheduling the schedulable

every 200 steps.  If we now decide to change this interval this affects

the whole simulation as all clients (other steppables) are now

influenced by this.



The same happens if you schedule extra objects which don't use the

randomgenerator itself or don't influence any of the other steppables!.

We saw this behavior when we introduced some new steppables to perform

some extra calculations so certain work wasn't duplicated in other

objects.  Seeds which initially had an interesting behavior for our

simulations showed a completely new behavior after these changes.



I don't know if this behavior is really intended or not?  But is there a

possible solution for it?

Personally I feel that the scheduler should have it's own

randomgenerator.  It won't solve all possible situations, but could

simplify others.



One of the things not solved is that the scheduling of steppables with

different orderings will still differ if you add more steppables with

the same ordering.  But this won't influence the actual simulation if

these steppables don't interfere.



I hope I could describe the "issues" we are having sufficiently so they

are clear and would like to hear if this is the intended behavior or if

there is a simple way to remedy this.





Kind Regards,

Bruno



-- 

Bruno Van Den Bossche

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http://www.ibcn.intec.UGent.be