Question: List elements not being updated in stochastic process simulation

Hi there,

I'm trying to simulate an stochastic SIR model following the Gillespie algorithm, as described here [1].


When trying to update each process' probabilities, it looks like Maple is not updating their values. Although each element of the lists S, I and R is updated the ai lists are not updated.

For example, for a given index i

a2[i]:= m*S[i]:

takes the same value for every i, regardless of the value of S[i].

Can anybody tell why this is happening or what's wrong with the worksheet? This is the attempt:


On the other hand, I tried making things more clear through a couple of procedures. However, when it comes to the point where a random number with an exponential distirbution is computed:

Rexp := RandomVariable(Exponential(mu)):

it looks like Maple is unable to evaluate mu. But having a look at the Variables explorer, it has a defined value, indeed.

So what's wrong in the worksheet? Thi is the attempt:





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