Variable value for each timestep VENSIM PLE

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luisehuberta
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Vensim version: PLE

Variable value for each timestep VENSIM PLE

Post by luisehuberta »

Hi there!

I have a question regarding putting in variable values for each time step for a supply chain simulation over the course of one year. Basically I have 27 countries with production value as a variable, export and import as inflow and outflow with each other country varying each month of the year. This model will then be used in a sensitivity analysis where I will alter the input factors - but for that I need a sufficient model than runs smoothly.

Any help is appreciated! I am a complete VENSIM PLE beginner and very happy for any help I can get!

Looking forward to your responses. Thank you in advance!

Greetings from Germany, Marie
Administrator
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Re: Variable value for each timestep VENSIM PLE

Post by Administrator »

I don't understand what you are asking for help with.

If you have 27 countries, you would really be better off using Vensim Pro as it allows subscripts/arrays which will allow you to model all 27 countries at the same time with a single model structure.

Vensim PLE also does not have the ability to do sensitivity analysis.
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luisehuberta
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Posts: 6
Joined: Tue Feb 09, 2021 10:12 am
Vensim version: PLE

Re: Variable value for each timestep VENSIM PLE

Post by luisehuberta »

Thank you for your quick reply.

What I want to simulate is a trade relationship so let's say Austria will get an inflow of product from Germany which differs every month (January=0, February=200, March=300, May=176 and so on). And then I wish to alter the input factors and analyse the overall reaction of the whole model. I am not sure if I have access to the Pro Version through my university - so the PLE Version is useless for what I want to do?
tomfid
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Re: Variable value for each timestep VENSIM PLE

Post by tomfid »

PLE is designed for learning about dynamics, not for detail-oriented work. However, if you can simulate the 27 countries independently, you might make it work. You could put the demand stream in a lookup (as a function of time). Then you could load different streams from changes files (.cin) for testing.
luisehuberta
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Vensim version: PLE

Re: Variable value for each timestep VENSIM PLE

Post by luisehuberta »

So you mean integrate a Lookup table with the values for the different imports in the different time steps? Why would I need to model each country independently though?
tomfid
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Re: Variable value for each timestep VENSIM PLE

Post by tomfid »

Correct.

I guess you don't have to model the countries independently, but copy-pasting the structure 27 times to do them together without arrays sounds painful.
luisehuberta
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Vensim version: PLE

Re: Variable value for each timestep VENSIM PLE

Post by luisehuberta »

Okay thank you so far! So in a Lookup table, can I not only tell VENSIM the different values, but also the origin of each value? In order to actually model a trade relationship
tomfid
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Re: Variable value for each timestep VENSIM PLE

Post by tomfid »

A lookup has one input (e.g., time in this case) and one output.

You can create arrays of lookups, where the subscript elements represent other attributes (country, commodity, etc.).
luisehuberta
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Vensim version: PLE

Re: Variable value for each timestep VENSIM PLE

Post by luisehuberta »

And there is no other way to work around that using VENSIM PLE?
tomfid
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Re: Variable value for each timestep VENSIM PLE

Post by tomfid »

In PLE you have 2 options:

- Build a generic model of a single country, and then load different values of parameters and the demand lookup from a changes file, with 27 distinct copies of the file.

or

- Build the model for one country, then copy-paste it 26 times. You could use generic lookups for the initial instance, but then modify the data using a change file (you'd only need one, which would be a little more convenient).

If you need a 27 x 27 trade matrix, I think these approaches are impractical. It would be easy to handle that with arrays in Pro/DSS.
luisehuberta
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Re: Variable value for each timestep VENSIM PLE

Post by luisehuberta »

Thank you! Well but what I need is to also analyse the relationship between the countries. So I need them all in one model. I will not be able to finance the pro version, is there not a free trial version of the Pro?
tomfid
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Re: Variable value for each timestep VENSIM PLE

Post by tomfid »

There are deep discounts for academic and public research purposes. You can shoot us an email at vensim at vensim.com for a quote. Possibly there's an unused copy at your institution?
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