Alejandro Cevallos avatar image
Alejandro Cevallos asked Matt Long commented

Variability in the output of the source

I made a simulation that consists of several items, in which I have 3 sources that are programmed with different distributions of arrival. By running the simulation I get three output values respectively, but at the time I erased a processor part of the simulation, the output values of each source vary compared to previous values. Why does this happen if I did not change anything in the sources?

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Ralf Gruber avatar image Ralf Gruber ♦ commented ·


did you use the same random stream no. for the distribution in all objects? That would explain that behavior. If not please provide the model to us.


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Adrian Haws avatar image Adrian Haws commented ·

@Alejandro Cevallos

Is this question about a modified version of the model you posted here?

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1 Answer

Matt Long avatar image
Matt Long answered

I'm guessing you haven't specified specific random number streams for each of your Sources? If that is true then this is expected behavior if your deleted processor was using a random number stream (by calling a statistical distribution command) or if by deleting the processor you changed the series/ordering of events.

FlexSim initializes random number streams on reset. By default all of the random number distributions use stream one, which means they're all pulling from the same stream of numbers. If the order is change by adding or removing calls to the number stream, the results will change. You can visualize it like this.

Imagine this is our random number stream as initialized by FlexSim.

4.325 6.24 8.543 2 14.253 3.6 1.234

If Repeat Random Streams is checked in the main menu, these numbers will be the same each time you hit reset. When the first call to the stream is made, the return value is 4.325, the second call is 6.24 and so forth. If all of the objects are sharing the same stream, then changing the order of events or adding/removing calls to the number stream will cause objects to receive different numbers.

If it's important that this doesn't happen, you can specify a stream for each object, that way they are pulling from their own number stream that won't be messed with by any of the other objects. The stream is always specified as the last parameter:

exponential(0, 5, 1); //Stream 1
exponential(0, 5, 2); //Stream 2

By default a model initializes 100 random number streams. This can be changed through the Model Settings window in the Edit menu.

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