Ventana software support forum

Thank you so much. It works perfectly!

Thank you very much for your reply. Please see the attached sample. To reduce file size, I just put 30 scenarios. Each row represents one scenario for 31 data points from 1990 to 2020. I would be very grateful if you could let me know how I can implement it in Vensim Professional. Thank you so much....

Hi Tom and colleagues, Happy New Year! I have a question about using time series data for sensitivity analysis. I know the 'File' option in Sensitivity Simulation Setup can be used for setting different values of model variables (parameters). But, what if a model variable is not a constant, but inst...

Hi Tom, please may I follow up with you on this? Many thanks. I see. In that case, it does seem sensible to do some kind of combinatorial resampling from the individual columns. Unfortunately, the Vensim file sensitivity isn't set up to do this, but I'll take a look - it might be simple to implement.

Thanks a lot Tom for helping. I look forward to hearing from you.

Hi Tom, many thanks for your helpful reply. I agree with you that the joint distribution should be more proper than marginal distribution if the parameters are correlated. But in my case, they are not correlated. Their posterior distributions were obtained from separate independent models. And there...

Hi Tom, happy new year and I hope you had a great holiday season. I have a question about the "File" option in the Sensitivity Simulation Setup. I want to run Monte Carlo simulations of my model by randomly drawing samples from a distribution of Parameter A, a distribution of Parameter B, ...

Hi Tom, Hope you have been doing great. I have a question about using the term "probabilistic" in the context of system dynamics. For a given system dynamics model, suppose its structure is considered deterministic, and its parameters are considered random. After using empirical data to es...

Hi, for academic papers, what is the recommended way of citing Vensim?

Thank you very much.

Hi, Is it possible to extract a value at a specified time from a stock? For example, my stock has the following values: Year 2000, stock = 0 Year 2001, stock = 1 Year 2002, stock = 2 Year 2003, stock = 3 ... Year 2029, stock = 29 Year 2030, stock = 30 Is there a straightforward way to extract a valu...

Hi, is it possible to use both File and the built-in distribution for one sensitivity analysis? For example, a user-defined file is used for parameters A and B, and the built-in Random Normal and Random Uniform are used for parameters C and D. Based on this setup, run sensitivity simulation. This do...

Hi JJ, it is still something exploratory. I agree that it is difficult to choose between them, but it is great to have these options available.

Hi Tom, thank you so much for setting up these models, which provide very helpful insights into their inherent dynamics and the emergent outcomes.

To reflect the high variance of the post-retrofit period ("on-hold" period), would the original first-order delay treatment in the picture above be a reasonable approximation?

Thanks Tom for your insight. So what would be a reasonable simplification here if the "on-hold" segment of the model is still needed?

It may be necessary to go to this level in some cases such as infrastructure development, power plants, etc. Hence the distribution of their ages and properties at yearly level would have relevance from policy-making perspective. I'm still not convinced of the policy relevance of preserving every de...

Hi Tom, I feel that this has to be regarded as a 2-dimension problem. So maybe subscripts [i,j] and VECTOR ELM MAP should be used?

tomfid wrote: ↑Fri Nov 02, 2018 2:41 pm You could map the return flow from age x to age x+d of the main stock, right?

Hi JJ, thank you so much for your example model. I was hoping to use 2 subscripts but was not able to figure it out. Your approach is enlightening. I have not fully understood the logic behind your model, so I am still studying it carefully. For now, a quick question please: does this model allow wi...

Hi Tom, thanks for your suggestion. However, I do not think that solves the problem, because when those items are being on hold for the required period, they shall keep aging as usual rather than being "frozen". If an infinite-order delay is used, the outcome is that a 5-day-old item enter...

Hi Tom, I came across an old post where the question raised was almost exactly the one I am having now and you gave a very enlightening solution using arrays. I have attached it here for easy reference. And the post is: https://www.ventanasystems.co.uk/forum/viewtopic.php?f=2&t=5287 Essentially,...

Hi Tom, thanks for your reply. I just updated my Vensim Pro to the latest version 7.3.5. But the problem remains. The following is all information contained in my .rep file after running a payoff optimization. Is there a way to show the full information, e.g. Goodness of Fit, etc? The payoff is -20....

Hi,
Would anyone share some experience in this, please? Many thanks.

Hi,

This might be a trivial question - why my payoff reporting file does not contain information on Goodness of Fit, Theil Statistics, and Absolute Errors? It only has information on Metadata & Contributions.

Many thanks.

Hi Tom, Thanks for your advice. I meant the samples (datapoints). They are all exactly the same, regardless of the payoff value being set as 1.92, 3,84 or 6.63. However the bounds reported in the sensitive.tab are different, as follows: :COM The base payoff is -7.46857 : SENSITIVITY = PAYOFF_MCMC = ...

Hi Tom, I was trying to compare the samples resulting from standalone MCMC and payoff sensitivity MCMC, by following the Reference Manual (MCMC Options). While specifying standalone MCMC as the Optimizer is straightforward, I have encountered a problem with specifying MCMC as a method of payoff sens...