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Is Negexp random

Pioneer
Pioneer

Hi everybody, I am creating a simple model that has both in the source and single processes a negexp time, with only yhe beta(average) specified. I've seen that if I do the same model in two different files, the results changes, even if everythingis (or should be) the same. Is this due to the fact that the negexp has a random part that makes these model's results different? Or did I make some error? I have attached two models with different results.

7 REPLIES

Re: Is Negexp random

Phenom
Phenom

unfortunately you have posted models, created with a non commercial license,

which cannot be opened with a commercial (professional) license.

 

Therefore I cannot look at your models.

 

Nevertheless what you are facing has to do with individual random numbers for objects.

 

(s. help extract from v14. help)

Unbenannt.png

 

Betreff: Is Negexp random

Gears Phenom Gears Phenom
Gears Phenom

In addition to simulator's response (I also cannot open your models, same problem):

 


You may, at times, wish to use the same random numbers for two objects. You might, for example, want to compare two production lines, and you insert two identical Source objects, which are going go create identical parts within identical intervals. To accomplish this, you need to set the random number seed value for the affected material flow objects to the same value, i.e., assign the same value to the attribute RandomSeed. When you create a new object, for example by inserting it into a simulation model, Plant Simulation automatically assigns a unique random number seed value to this object.

So you can check out the attribute RandomSeed of the Source and SingleProc in your models and they will most likely be different. The RandomSeed attribute is set automatically and depends on the sequence in which you insert objects into your model. If you exactly replicate the creation of the first model, you will get the same results (even though of course negexp is a random distribution, with only one parameter, the "average").

Hope this helps,
Alex

____________________________________________________________
Alex Dilg, Consultant at SimPlan AG (www.SimPlan.de)
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Betreff: Is Negexp random

Pioneer
Pioneer

Thanks, now I understand the difference. Is it possible to set manually this random number?

Betreff: Is Negexp random

Gears Phenom Gears Phenom
Gears Phenom
Yes, you can set the attribute „RandomSeed“ manually, if you have to.
____________________________________________________________
Alex Dilg, Consultant at SimPlan AG (www.SimPlan.de)
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Betreff: Is Negexp random

Pioneer
Pioneer

Thanks!!!

 

Modify:

 

I have changed the attribute RandomSeed, but the results didn't change at all. They are still different. Could there be another difference due to the negexp function?

Betreff: Is Negexp random

Gears Phenom Gears Phenom
Gears Phenom

Hi NicoF,

if you change the RandomSeed of a station with a random distribution, then also the result should change (unless you have some strange settings-combination). And if all settings and also the RandomSeeds are the same, I think the models should yield the same results. There is also an attribute of the EventController "RandomNumbersVariant", but this is set to 1 by default, so it should be equal in your 2 models.

Can you post some screenshots of your models? Is SimTalk with random-distributions involved? Have you used the "Compare Models" option to see whether your models are really identical?

Regards,
Alex

____________________________________________________________
Alex Dilg, Consultant at SimPlan AG (www.SimPlan.de)
This post was good and/or helpful to you? Please provide some Kudos, thank you!

Betreff: Is Negexp random

Pioneer
Pioneer
I have re-checked it and now they are the same. Thanks for all the answers!!