Search found 3259 matches

by tomfid
Wed Jun 09, 2021 3:52 pm
Forum: Vensim
Topic: model calibration
Replies: 4
Views: 1426

Re: model calibration

It's on the list for the graphs in the new interface.
by tomfid
Mon Jun 07, 2021 2:42 pm
Forum: Vensim
Topic: Lookup for time series
Replies: 3
Views: 99

Re: Lookup for time series

1. The Help system has a lot of material on lookups. https://vensim.com/documentation/usr08.html
2. Quick start video: https://vimeo.com/55318481
by tomfid
Fri Jun 04, 2021 6:31 pm
Forum: Vensim
Topic: Getting Multiple Values with GET XLS LOOKUP
Replies: 3
Views: 88

Re: Getting Multiple Values with GET XLS LOOKUP

You could do this with 2 lookups, using copy/paste. x axis is scenario #, y axis is min or max temp. Copy the data from the columns of the spreadsheet and paste it into the lookup (there's an import button). I think you'll have to transpose from columns to rows and get rid of the intervening text co...
by tomfid
Tue Jun 01, 2021 6:27 pm
Forum: Vensim
Topic: Sensitivity Graphs and Confedence Intervals
Replies: 2
Views: 69

Re: Sensitivity Graphs and Confedence Intervals

The line in this case is your base run for Test A. That suggests that the parameters of the sensitivity analysis are not centered around the base case.

I guess the reason we only see the 50th percentile here is that the 75/95/100 values are set to white?
by tomfid
Tue Jun 01, 2021 4:22 pm
Forum: System Dynamics Discussion
Topic: Dealing with Expectations or forward-looking behavior
Replies: 1
Views: 433

Re: Dealing with Expectations or forward-looking behavior

This is a pretty broad question - can you suggest a specific situation?
by tomfid
Tue May 25, 2021 7:08 pm
Forum: Vensim
Topic: the procedure entry point getfullpathnamew could not be located in dynamic link library C:\program files\vensim\venple32
Replies: 8
Views: 193

Re: the procedure entry point getfullpathnamew could not be located in dynamic link library C:\program files\vensim\venp

Scroll to the bottom of
https://vensim.com/faq/
and look for
On running Vensim, I get the error “api-ms-win-core-version-l1-1-1.dll is missing”.
by tomfid
Sat May 22, 2021 1:04 am
Forum: Vensim
Topic: Lookup error
Replies: 2
Views: 157

Re: Lookup error

It's really just a warning. It indicates that the input to the table exceeds the x-axis you've specified. In your case, the max x value is 2, so the input must exceed that at time 1. It's not necessarily a problem, but good to know that it's happening.
by tomfid
Fri May 07, 2021 9:07 pm
Forum: Vensim
Topic: Vensim PLEx64 installation
Replies: 5
Views: 282

Re: Vensim PLEx64 installation

Is this Windows 7?
by tomfid
Wed May 05, 2021 2:46 pm
Forum: Ventity
Topic: combining referenced stocks within a cohort model
Replies: 2
Views: 238

Re: combining referenced stocks within a cohort model

As a matter of process, it might be more productive to get a single cohort working the way you want it to before adding a lot of relationship complexity.
by tomfid
Wed May 05, 2021 2:45 pm
Forum: Ventity
Topic: combining referenced stocks within a cohort model
Replies: 2
Views: 238

Re: combining referenced stocks within a cohort model

1) The normal way to aggregate things would be to use a collection to compute Sum(Money). However, that would require a single generic cohort type with 3 instances, rather than the 3 distinct entitytypes that you're using. If you really need 3 different entitytypes, rather than one type with 3 insta...
by tomfid
Tue May 04, 2021 9:24 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

One option for preserving the logistic is to put a ceiling on the input to the exponential. For example, instead of EXP(x) use EXP(MIN(100,x)).
by tomfid
Fri Apr 30, 2021 3:09 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

I notice that the computation of growth variation uses DELAY FIXED initialized to 0. This means that any growing scenario will be penalized initially, because the growth rate starts at a nonzero value in year2020.
by tomfid
Fri Apr 30, 2021 2:03 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

A good test would be to manually set the parameters to what you think is a good solution, and see if that yields a payoff that is actually better. That would be tedious with the annual decision points, but you could reduce the size of the vector so that decisions are made at 5-year intervals and int...
by tomfid
Fri Apr 30, 2021 2:01 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

I think the optimizer is perfectly capable of handling a situation like this with appropriate inputs.

The logistic penalty probably causes floating point errors because EXP(x) overflows for x greater than about 300 (or 30 in single precision). x^2 or ABS(x) is usually a better choice.
by tomfid
Wed Apr 28, 2021 4:32 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

Some observations on the setup: - The model has no units, which is not best practice. - Payoffs are normally flows, so when you include Cumulated Costs in your payoff, you're using not only the final value, but all the earlier values, which means that the early part of the simulation is heavily weig...
by tomfid
Wed Apr 28, 2021 4:11 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

By default, Vensim uses a modified Powell search. See http://www.it.uom.gr/teaching/linearalgebra/NumericalRecipiesInC/c10-5.pdf for a good explanation. For complex surfaces, doing lots of random multistart simulations is highly recommended. You can also use the Markov Chain Monte Carlo algorithm fo...
by tomfid
Mon Apr 26, 2021 6:51 pm
Forum: Ventity
Topic: Optimisation
Replies: 7
Views: 641

Re: Optimisation

If you're seeing this, it might be a path permission issue. 2021-04-26_12-51-27.png There are two copies of the Ventity samples installed. You might try the one in your local user documents folder, rather than users\public. If that also fails, perhaps copy/paste the model directory to an unlocked lo...
by tomfid
Mon Apr 26, 2021 6:42 pm
Forum: Ventity
Topic: Optimisation
Replies: 7
Views: 641

Re: Optimisation

ventityOptSettings.png
ventityOptSettings.png (19.39 KiB) Viewed 449 times
There are some optimization control settings in the payoff dialog. Normally the Fractional Tolerance is the most productive to play with for controlling run length and precision of the result.
by tomfid
Mon Apr 26, 2021 6:38 pm
Forum: Ventity
Topic: Optimisation
Replies: 7
Views: 641

Re: Optimisation

The Wilshire model is working fine for me. What error are you seeing?
by tomfid
Mon Apr 26, 2021 6:28 pm
Forum: Vensim
Topic: Lookup tutorial video on Vensim site not there...
Replies: 2
Views: 233

Re: Lookup tutorial video on Vensim site not there...

All should be fixed now. Thanks again.
by tomfid
Mon Apr 26, 2021 5:25 pm
Forum: Vensim
Topic: Lookup tutorial video on Vensim site not there...
Replies: 2
Views: 233

Re: Lookup tutorial video on Vensim site not there...

Thanks for the notice. I just fixed it. I suspect that other links will be broken as well - probably a host or Vimeo change. I'll check everything.
by tomfid
Mon Apr 26, 2021 2:51 pm
Forum: Ventity
Topic: Optimisation
Replies: 7
Views: 641

Re: Optimisation

I'll take a look at the remaining issues.

When there are multiple payoff elements, the optimizer maximizes the sum of the variables, multiplied by the weights.
by tomfid
Fri Apr 23, 2021 9:39 pm
Forum: Vensim
Topic: How to change number of significant figures?
Replies: 3
Views: 292

Re: How to change number of significant figures?

It's working for me, but I'm using a recent alpha build. I think that means we've fixed it for the next release, but I'll double check.
by tomfid
Fri Apr 23, 2021 2:37 pm
Forum: Vensim
Topic: Optimization with variables as parameters and varying constraints
Replies: 13
Views: 695

Re: Optimization with variables as parameters and varying constraints

You can enforce constraints with penalty terms in the payoff. For example:

Penalty = MAX(0, Actual Stock - Max Stock Constraint) * exceedence value

Then make that a (negative) policy payoff term.
by tomfid
Wed Apr 21, 2021 9:30 pm
Forum: Vensim
Topic: How to change number of significant figures?
Replies: 3
Views: 292

Re: How to change number of significant figures?

It calculates in double precision, but the Table tool truncates the precision. You can change this by right-clicking the tool for options. If you switch to "Scientific" you can use C printf-style format strings to set the precision. The dll has separate functions for single and double output. If you...