Random variables in Vensim PLE

marcow · Post by **marcow** » Mon Dec 22, 2008 9:44 am

Hi,

I have a model with a random (normally distributed) variable. If I run the model several times, Vensim generates the same valuesfor my random variable in every run. Is there a possibility to change this? Can I run the model several times automatically with different random values?

Just for information: I am using Vensim PLE 5.5d

Marco

Post by **Administrator** » Mon Dec 22, 2008 11:46 am

You need to change the noise seed to generate different results.

Hope this helps.

Tony.

LAUJJL · Post by **LAUJJL** » Mon Dec 22, 2008 2:19 pm

One solution would be to make the seed equals for instance to the time of the day in seconds. Probably a solution would be to get the time from Excel, eventually through VBA. I am not sure if it is possible. This way every time you launch a simulation, the seed bould be modified automatically.
I personally have not that problem as I use subscripts for the different simulations. Every simulation has different random values even with the same seed value.
The model is joined. You can view it with the model reader, as you have only the PLE version.
To build models with subscripts you need at least the pro version.
Regards.
JJ

marcow · Post by **marcow** » Mon Dec 29, 2008 2:24 pm

thank you very much, the information about the "noise"-variable helped me a lot.

Unfortunately I can't open the model (I think because I am using the PLE-Version). The problem if I get the time from Excel is, that I still have to launch the simulation many times manually. I would like to launch it automatically (and get a table with all data of an output-variable) as I don't want to click so many times.

The problem is, that I am not sure, if the PLE plus-Version will help. As far as I have seen in the manual of Vensim, the PLE plus-Version only provides the sensitivity-analysis, but i would like to see the "raw"-data of every launch and export them...

Post by **Administrator** » Mon Dec 29, 2008 3:04 pm

>> The problem is, that I am not sure, if the PLE plus-Version will help. As far as I have seen
>> in the manual of Vensim, the PLE plus-Version only provides the sensitivity-analysis, but i
>> would like to see the "raw"-data of every launch and export them...
You should be able to do this fine with PLE Plus. All you do is run a sensitivity simulation, and make sure the noise seed parameter is in the save list of variables you wish to examine later.

There is a full list of the various capabilities of Vensim at
http://www.vensim.com/comparison.html

Tony.

marcow · Post by **marcow** » Wed Feb 11, 2009 6:49 pm

now i purchased PLE plus and the sensitivity simulation is working great.

Does anybody maybe know how to export sensitivity results to excel? I only can copy & paste the different graphs and charts, but can't copy the data. I need at least the mean of my variable at the end of the simulation or sth similar.

Post by **Administrator** » Wed Feb 11, 2009 7:07 pm

Create a save list that contains the variables you are interested in.

Now run your simulation.

Click Model->Export Dataset and you should be able to export the values for each simulation to a .CSV file. From here you can open in Excel and use any of the statistical functions.

Hope this helps.

Tony.

marcow · Post by **marcow** » Thu Feb 12, 2009 8:00 am

i tried to open the vdf-file and did not convert it to csv... Now everything is working fine. Thank you very much, you helped me a lot

Marco