How to run simulation with lookup table change

Use this forum to post Vensim related questions.
Post Reply
andreas.vitikan
Junior Member
Posts: 2
Joined: Sun Sep 09, 2018 12:34 pm
Vensim version: PLE

How to run simulation with lookup table change

Post by andreas.vitikan »

I am running Vensim PLE x64 version 7.2a on Windows 7 x64. I am trying to learn more about the software Vensim (as well as system dynamics) and am trying to explore the World3 model from the Vensim website http://vensim.com/model-analysis-world-dynamics/ (subfolder WRLD3-03, model wrld3-03+.vmf). I have read from the included Help with the software the User Guide/a hands-on example (chapter 3) and building a simulation model/simulating the model (chapter 6) but I'm still unsure how to do this or what I am doing wrong. I want to the run the simulation with changes to some of the lookup tables.

With the model freshly extracted (just as downloaded - no modifications), I open the World3 model in Vensim, I type in "baserun" under "Simulation results file name" and I click "Simulate". Everything good so far. After that I type in a different simulation result file name, say "experiment1" and I click Sim Setup. I modify the lookup tables that interest me (say for example "assimilation half life mult table" under "Persistent Pollution") and I click "Simulate". The simulation results file name toolbox goes back to displaying the "Simulation" and "SyntheSim" buttons and it seems as if the modifications were accepted. However if I check the lookup table I modified using the Equations tool it shows the original values of the lookup table and not my modified ones.

I also tried achieving this using SyntheSim but haven't had much luck either. I type in a results name - say "experiment2" and I press SyntheSim. All the variables now have sliders, moving the sliders changes the simulation results in real time. I double click the lookup table and modify it, but after that I'm stuck on how to save the run so I can compare it with the base line. If I Click "Stop Setup" I lose all modifications and if I save it, the simulation results file name toolbox does not revert to its default state - with the "Simulation" and "SyntheSim" buttons. I can't access the baseline simulation data and even the model interface (Where all the stocks and loops and valves are displayed) seems to behave differently than the "default state".

I have read the included Vensim manual but cannot figure this out, what am I doing wrong here?
tomfid
Administrator
Posts: 3806
Joined: Wed May 24, 2006 4:54 am

Re: How to run simulation with lookup table change

Post by tomfid »

When you modify a lookup in setup mode or Synthesim, the changes are transient. This is deliberate, to preserver the original model structure. (This is one huge downside to spreadsheets - it's easy to make inadvertent modifications and lose track of your original version.) The results will be in the dataset (run) that you generate. As long as you have your new run loaded (Control Panel>Datasets tab), which it sounds like you do, any tool (graph, table, etc.) should reflect your changes.

If you want to verify this, load your baserun and modified run as the first two datasets in the list, and use the Runs Compare tool to check for differences.
andreas.vitikan
Junior Member
Posts: 2
Joined: Sun Sep 09, 2018 12:34 pm
Vensim version: PLE

Re: How to run simulation with lookup table change

Post by andreas.vitikan »

Thanks alot for the reply! I think I understand more about how datasets and different simulations work, and indeed the Runs Compare tool shows the new run with the changed lookup table values versus the originals.

I also didn't know about the Control Panel > Datasets tab, that's very useful, and it all makes sense now. It shows what runs are loaded and in what order and you can manage them from there, brilliant. Thanks again!
tomfid
Administrator
Posts: 3806
Joined: Wed May 24, 2006 4:54 am

Re: How to run simulation with lookup table change

Post by tomfid »

Hopefully a lot of this is covered in https://vensim.com/building-a-simple-vensim-model/

Glad it's working!
Post Reply