Search found 2998 matches

by tomfid
Mon Apr 20, 2020 1:08 pm
Forum: Vensim
Topic: math operations on simulated scenario results
Replies: 3
Views: 446

Re: math operations on simulated scenario results

But what is the purpose of these operations?
by tomfid
Sat Apr 18, 2020 9:01 pm
Forum: Vensim
Topic: Help with usage of MCMC
Replies: 11
Views: 764

Re: Help with usage of MCMC

Please do - I'm curious to see how this works out.
by tomfid
Sat Apr 18, 2020 7:01 pm
Forum: Vensim
Topic: Help with usage of MCMC
Replies: 11
Views: 764

Re: Help with usage of MCMC

OK ... here's the issue. At present you have a lookup containing the data, used to generate real_report. The model samples the overwintering population on day 30 to generate "report". The payoff compares the two and computes a sum of squares. So far so good. Problem #1: the data in real_report isn't...
by tomfid
Fri Apr 17, 2020 10:17 pm
Forum: Vensim
Topic: Help with usage of MCMC
Replies: 11
Views: 764

Re: Help with usage of MCMC

You can definitely anneal prior to generating the sample - you just want to be sure that the temperature is down to 1 before the end of the burnin period.

I don't see your attachments.
by tomfid
Fri Apr 17, 2020 8:42 pm
Forum: Vensim
Topic: Help with usage of MCMC
Replies: 11
Views: 764

Re: Help with usage of MCMC

I think the first question is probably whether your payoff is properly weighted. With Normal distributions, it should have an expected value roughly equal to the number of points.

Can you share your setup - if not the model and data, at least the .vpd and .voc files and a payoff report (.rep)?
by tomfid
Tue Apr 14, 2020 7:44 pm
Forum: Vensim
Topic: Equivalent function needed in Vensim
Replies: 4
Views: 499

Re: Equivalent function needed in Vensim

Right. That could make the syntax of the GRAPH function: GRAPH( inputVar, xmin, xmax, [vector of points] ). I think the Min/Max/Zoom items may be just for display. The big question is probably whether the 3rd argument should be xincrement or xmax. I agree that embedding constants in equations is bad...
by tomfid
Tue Apr 14, 2020 5:45 pm
Forum: Vensim
Topic: Equivalent function needed in Vensim
Replies: 4
Views: 499

Re: Equivalent function needed in Vensim

Is this basically a lookup table?
by tomfid
Fri Apr 10, 2020 1:09 pm
Forum: Vensim
Topic: How do I remove toolbar labels?
Replies: 2
Views: 402

Re: How do I remove toolbar labels?

That might be one of the cases where you actually do need to exit & relaunch to get it to work. If not, it's a bug.
by tomfid
Thu Apr 09, 2020 3:43 pm
Forum: Vensim
Topic: Low optimisation speed
Replies: 11
Views: 903

Re: Low optimisation speed

If you have some time to experiment, I'd be interested in some timing comparisons between your Ryzen machine and my Intel-based workstation.
by tomfid
Wed Apr 08, 2020 4:49 pm
Forum: Vensim
Topic: using IF THEN ELSE for creating max/min values
Replies: 5
Views: 483

Re: using IF THEN ELSE for creating max/min values

It's probably a parentheses nesting problem. It's better if you make the sin wave a separate variable, then clip it in another equation. Also, the parameters should be made into variables so that units balance. For example: sinwave = amplitude*SIN( (Time-PhaseShift)/period*2*3.1415926 ) clippedSinwa...
by tomfid
Sat Apr 04, 2020 6:26 pm
Forum: Vensim
Topic: External function version mismatch
Replies: 12
Views: 798

Re: External function version mismatch

Can the existing setup be preserved via addition of _VDFX to the compiler preprocessor definition list, or are there other things that need to change?

One option would be to do a diff on the new shipping venext.c example vs. your venext.c and see what differs.
by tomfid
Fri Apr 03, 2020 12:29 pm
Forum: Vensim
Topic: External function version mismatch
Replies: 12
Views: 798

Re: External function version mismatch

Right - you need to modify your .dll project to use the new copy of vensim.h etc. (typically in users\public\comp).
by tomfid
Fri Apr 03, 2020 1:06 am
Forum: Vensim
Topic: External function version mismatch
Replies: 12
Views: 798

Re: External function version mismatch

This means you have an external function library loaded that needs to be recompiled with the new version's headers.

If you're not using it, you can delete the reference at Tools>Options>Startup.
by tomfid
Thu Apr 02, 2020 6:20 pm
Forum: Vensim
Topic: Use of MCMC
Replies: 5
Views: 537

Re: Use of MCMC

Will look when I can. Your description sounds right though. Just watch out for missing minus signs - easy mistake to make.
by tomfid
Thu Apr 02, 2020 5:09 pm
Forum: Vensim
Topic: Use of MCMC
Replies: 5
Views: 537

Re: Use of MCMC

Sorry - requires some thought and I've been ultra busy. 1. This is not automated yet, so you have to create an equation to express your prior. Here's an example. Suppose I have a policy effect parameter. If you don't know what its value could be, just that it's >0, you could use the improper log-uni...
by tomfid
Thu Apr 02, 2020 4:41 pm
Forum: Vensim
Topic: Function for reading from a vdf file
Replies: 6
Views: 462

Re: Function for reading from a vdf file

Another trick that I used ages ago, before GET VDF existed, was to create a separate model containing just a pair of variables that transform the base value into a data variable with a different name. Something like: Main model: price of cheese = {some simulated stuff} data price of cheese {data var...
by tomfid
Thu Apr 02, 2020 4:09 pm
Forum: Vensim
Topic: Function for reading from a vdf file
Replies: 6
Views: 462

Re: Function for reading from a vdf file

Great! It's been a while since I've done this, but there's always a chicken-egg problem when the Base run that you're looking up comparison values from doesn't exist yet. I think I've solved this with some kind of IF THEN ELSE( base data = :NA:, 0, base data) logic, but I don't remember the details....
by tomfid
Thu Apr 02, 2020 2:19 pm
Forum: Vensim
Topic: Function for reading from a vdf file
Replies: 6
Views: 462

Re: Function for reading from a vdf file

I think you want GET VDF DATA.
by tomfid
Wed Apr 01, 2020 4:34 pm
Forum: Vensim
Topic: Customized Analysis Toolset
Replies: 3
Views: 407

Re: Customized Analysis Toolset

I agree - this worked until very recently. We'll have a fix soon.
by tomfid
Mon Mar 30, 2020 12:47 pm
Forum: Vensim
Topic: TIME STEP and historical data
Replies: 14
Views: 747

Re: TIME STEP and historical data

If you think about a run with 4 time steps, the random draws might be Time 1 2 3 4 Value 3 8 2 6 If you halve the time step, you get Time 0.5 1 1.5 2 2.5 3 3.5 4 Value 3 8 2 6 1 7 7 9 The value 2 now occurs at time 1.5 instead of time 2, etc. In a real model, it's more complex than that, because you...
by tomfid
Mon Mar 30, 2020 12:31 pm
Forum: Vensim
Topic: TIME STEP and historical data
Replies: 14
Views: 747

Re: TIME STEP and historical data

Time step will have a big effect on any randomness - if you draw twice as many values, you get a completely different realization of the random streams. To calibrate a model with random inputs, you really need to look at the performance over an ensemble of simulations, rather than a single run. This...
by tomfid
Sun Mar 29, 2020 4:09 pm
Forum: Vensim
Topic: TIME STEP and historical data
Replies: 14
Views: 747

Re: TIME STEP and historical data

The best thing to do is create some custom graphs that compare the model to the data, and then do some hand calibration to see what's going on.
by tomfid
Sun Mar 29, 2020 4:08 pm
Forum: Vensim
Topic: TIME STEP and historical data
Replies: 14
Views: 747

Re: TIME STEP and historical data

If shrinking the time step is changing the payoff, that's probably a sign that it's also changing the dynamics, and that in turn is changing the fit.

The choice of time step really shouldn't have anything to do with the data interval.
by tomfid
Sat Mar 28, 2020 10:12 pm
Forum: Vensim
Topic: Vensim DSS Crashes on macOS
Replies: 5
Views: 432

Re: Vensim DSS Crashes on macOS

I think this might be a bug in the payoff reporting that we've fixed in development already. If so, the .out file written should still contain your final parameters, so you can rerun the endpoint solution.