Ventana software support forum

Hi
I have just imported a Vensim model in Ventity. Does Ventity accepts é or ‘ in names. What are the limitations in names. I want to see if it is not too difficult to import a model, and see if it reduces the size of the .vdfx files which are full of zeros. It should too run quicker having less zeros to calculate with.
Regards.
JJ

Punctuation generally won't work. Unicode like e-accent should. Do you have a Vensim source model we could test the translation on?

Yes I join a package file. It complies and runs quickly in Vensim but if one changes the subscript sim from s1 to (s1-s100) if is extermely slow to compile while still running quite quickly and generates a huge file. As the model is not finished and needs additionnal subscripts, i will not been able to run it with sim set to (s1-s100). To do ti I will be obliged to do it with Excell and the DLL. So i am interested in the file size generated by Ventity.
I cannot join the packaged file it does not accept vpmx extension. i join the modl and the cin file.

JJ

I assume the "sim" subscript is for running an ensemble of simulations simultaneously. Is there a reason sensitivity analysis wouldn't work for this?

HI Tom

I use parallel simulations for many reasons. My models having stochastic inputs, it is often necessary to run parallel simulations for optimization for instance. It could be possible to run a stochastic optimization, but i need to survey too not only average pay offs, but minimum too, and I can combine the payoff to maximize the minimum payoff. In the present case i do not use Vensim optimization techiques, I fist calculate optimal policies with dynamic programming techniques, from time 1 to 60, and from time 60 to time 180, i apply the policies calculated with parallel simulations, and studying the average result and minimum too. If i run only one simulation, the result is too much depending on the seed of the simulation. i need to verify the dynamic programing policies with stochastic simulations because the dynamic programming results use approximate techniques: reférence Bertsekas 'approximate dynamic programming. i can test the quality of my approximations on multiple simulations. But this generates huge files with plenty of zeros. But i can too use a simulation with only one parallel simulation and calculate the averages varying the seed by running multiple runs with Excel VBA even if this is rather laborious. But if you have other ideas, I am interested. JJ

Two quick thoughts:
- It should be possible to transform the utility function to express risk aversion. This wouldn't be quite the same as maximizing min(x), except in the limit, but it should be close.
- Then you could use the parallel version of Vensim, which is extremely fast if you have a lot of cores.

I did not know that there is a parallel vensim version that works on multiple cores. I have tested sensitivity analysis, and most of the time it had more drawbacks than advantages. but i can still try again. But i like solutions where you have control on what is calculated. I am anyhow very interested by accelerating the speed of runs. But from what %I know from parallelism it woks only with models specially structured. JJ

The parallelism is only across simulations in a sensitivity ensemble or optimization. Making a single run parallel in general is difficult.

For sensitivity runs and MCMC, the speedup is nearly linear in the number of cores. For Powell optimization, it's trickier, because parallel executions of tests in different directions tend to interfere with one another, unless the effects of the directions are basically independent.

Is it possible to have a documentation and price for the parallel vensim version? JJ

I sent you an email with a copy. If it doesn't arrive (spam filters may choke on it), let me know and I'll try another route.