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II.3.6. Generalized Stochastic Petri Nets

 

Generalized Stochastic PNs (GSPNs) have two different classes of transitions: immediate transitions and timed transitions. Once enabled, immediate transitions fire in zero time. Timed transitions fire after a random, exponentially distributed enabling time as in the case of SPNs. For timed transitions, the firing rate (i.e. the inverse of the mean time-duration) is, by default, marking independent, but the user can select a marking-dependent operation (the same way as for SPNs).

 

The simulation procedure is similar to the SPN case, the only difference occurring in the case of the immediate transitions that fire first; priorities/probabilities can be associated to these transitions, in order to resolve the conflicts.

 

The Diary facility opens a new window that displays (dynamically) the instant(s) when the next fireable transition(s) is (are) to fire.

 

The Scope facility opens a new figure window that displays (dynamically) the evolution of the selected performance indices. The final value of the global index shown by the Scope is identical to that displayed on request, at the end of simulation, when the user explores the Performance menu.


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