Search found 4006 matches

by tomfid
Wed Jul 02, 2025 2:56 pm
Forum: Vensim
Topic: Dump warning in log file
Replies: 1
Views: 20

Re: Dump warning in log file

I think you'll find some error logs in
C:\Users\yourname\AppData\Roaming\Vensim (shorthand %AppData%\Vensim )
by tomfid
Mon Jun 30, 2025 5:06 pm
Forum: Vensim
Topic: Multiple Equations for a Subscripted Variable HELP
Replies: 1
Views: 65

Re: Multiple Equations for a Subscripted Variable HELP

You've found a glitch that will be fixed in the upcoming release. You can't literally write, Price[sector,sector] = blabla but you can define subscript equivalents, fromSector <-> sector toSector <-> sector and then write, Price[ fromSector, toSector ] = blabla However, the equation editor glitch cu...
by tomfid
Mon Jun 30, 2025 3:49 am
Forum: Vensim
Topic: Lookup selection IF THEN ELSE()
Replies: 1
Views: 47

Re: Lookup selection IF THEN ELSE()

IF THEN ELSE(fluid=1, fluid1 lookup(input), fluid2 lookup(input))
by tomfid
Fri Jun 27, 2025 8:46 pm
Forum: Vensim
Topic: X IF MISSING / IF THEN ELSE
Replies: 2
Views: 178

Re: X IF MISSING / IF THEN ELSE

X IF MISSING is also more convenient if you have multiple data inputs in the equation.
by tomfid
Fri Jun 27, 2025 8:45 pm
Forum: Vensim
Topic: How do I use the compiled model with command script CMD
Replies: 3
Views: 101

Re: How do I use the compiled model with command script CMD

The other option is to package the model as a vpmx along with the compiled .dll.
by tomfid
Fri Jun 27, 2025 3:59 pm
Forum: Vensim
Topic: Export results from sensitivity analysis in xlsx format
Replies: 1
Views: 37

Re: Export results from sensitivity analysis in xlsx format

I don't recall if xlsx is supported, but CSV and tab-delimited are. Model>Export Dataset...

CSV opens into Excel by default.
by tomfid
Wed Jun 25, 2025 6:18 pm
Forum: Vensim
Topic: Copyright World3 Model
Replies: 2
Views: 1700

Re: Copyright World3 Model

I think you are certainly safe to extend and adapt World3 however you wish. Obviously it would be a courtesy to cite the original authors, whether or not it's strictly a legal obligation - which I'm sure you would. The Vensim license only applies to Vensim and ancillary components - anything you cre...
by tomfid
Fri Jun 20, 2025 8:36 pm
Forum: Vensim
Topic: Non-integer Poisson Warning
Replies: 2
Views: 565

Re: Non-integer Poisson Warning

It still computes the payoff; fortunately that works because it uses the LogGamma function as a continuous generalization of factorial. Should be harmless, though perhaps we should suppress excessive warnings.
by tomfid
Tue Jun 17, 2025 4:33 pm
Forum: Vensim
Topic: Resize first column of table?
Replies: 3
Views: 658

Re: Resize first column of table?

You're right ... as of at least 10.1.5 (Win) it was possible. So, regression ...
by tomfid
Tue Jun 17, 2025 4:06 pm
Forum: Vensim
Topic: Resize first column of table?
Replies: 3
Views: 658

Re: Resize first column of table?

I'm not sure it was possible, but obviously it should be. In the old gui, it was possible to right-click (ctl-click) the table tool to change the default width. Also, the runname should be in its own column. Ticketing for improvement ...
by tomfid
Sun Jun 15, 2025 10:14 pm
Forum: Vensim
Topic: What does fp_err_ctx do?
Replies: 2
Views: 880

Re: What does fp_err_ctx do?

These _should_ replicate an fp error. We'll take a look at the model. You might try turning on the payoff report, if it isn't already on, to reproduce.
by tomfid
Mon Jun 09, 2025 3:17 am
Forum: Vensim
Topic: Can I vary the NOISE SEED in the .vsc text instead of the checkbox?
Replies: 2
Views: 1764

Re: Can I vary the NOISE SEED in the .vsc text instead of the checkbox?

Not if you're using the File method. But every time you run an mcmc, it now generates a vsc that runs the sample with that box checked.

For other methods (multivariate, latin hypercube) you can add NOISE SEED=VECTOR(...) to the list as an alternative.
by tomfid
Fri Jun 06, 2025 2:42 am
Forum: Vensim
Topic: Does running Powell using DLL/Venpy generate '.out' file?
Replies: 2
Views: 2698

Re: Does running Powell using DLL/Venpy generate '.out' file?

The output should be the same. We'll have to take a look. Do you have a test case?
by tomfid
Thu May 29, 2025 4:55 pm
Forum: Vensim
Topic: MCMC with multiple chains and starting points
Replies: 3
Views: 2778

Re: MCMC with multiple chains and starting points

One way to assess what's going on is to look at the _distrib file that gets generated. If you filter out the final sample and plot a parameter against iteration, you can see how the distribution evolves.
by tomfid
Wed May 28, 2025 6:38 pm
Forum: Vensim
Topic: MCMC with multiple chains and starting points
Replies: 3
Views: 2778

Re: MCMC with multiple chains and starting points

No. There are three initialization methods: overdisperse, underdisperse, and hybrid (set by the MCINIT parameter). - over draws in the same way Powell multistart works, from a very broad powerlaw distribution (or uniform if both bounds are set); in the future, I'd like to modify this to draw from yo...
by tomfid
Wed May 28, 2025 3:42 pm
Forum: Vensim
Topic: Modeling simultaneous substitution flows
Replies: 3
Views: 4819

Re: Modeling simultaneous substitution flows

I'm puzzled by your statement that "defining simultaneous flows in two directions unintentionally inflates total demand. For example, demand moves from Brand B to Brand A, and then flows back to Brand B." In your example, demand is conserved. If demand shifts from A to B, the demand for B ...
by tomfid
Wed May 28, 2025 3:33 pm
Forum: Vensim
Topic: connectors to vars scrolled to not possible
Replies: 3
Views: 2521

Re: connectors to vars scrolled to not possible

Here's a possible workaround: Edit the equation for the destination variable. Add the source variable to the expression. When you exit, accept the request to add the source connection to the diagram. At this point, you'll have a straight arrow from source->destination. Navigate to the midpoint and c...
by tomfid
Mon May 26, 2025 11:52 pm
Forum: Vensim
Topic: How to rea-add part of a flow?
Replies: 2
Views: 4032

Re: How to rea-add part of a flow?

I think it's possible - use the flow tool to click on the valve, then click on the target (whitespace for a cloud, or another stock). You may have an unwanted arrowhead at this point, which you can turn off with a right-click.
by tomfid
Thu May 22, 2025 7:34 pm
Forum: Vensim
Topic: two constants as input, with a time delay on one constant
Replies: 2
Views: 3213

Re: two constants as input, with a time delay on one constant

Maybe this?
glucose in = infusion + endogenous
endogenous = STEP( endogenous rate, endogenous start time )
endogenous start time = 2
infusion = STEP( infusion rate, endogenous start time + infusion delay )
infusion delay = 4
by tomfid
Mon May 19, 2025 2:42 pm
Forum: Vensim
Topic: Help with Vensim
Replies: 3
Views: 3706

Re: Help with Vensim

There are also some video courses here https://vensim.com/video/
by tomfid
Thu May 08, 2025 8:17 pm
Forum: Vensim
Topic: Tracking stock attributes
Replies: 3
Views: 4470

Re: Tracking stock attributes

Great. Another place this comes up a lot is in tracking bonds and mortgages. There's usually a mix of terms, which makes the simpler first-order version attractive for strategic models, as in your case.
by tomfid
Wed May 07, 2025 4:09 pm
Forum: Vensim
Topic: How to model delayed flows due to unmet demand
Replies: 2
Views: 4426

Re: How to model delayed flows due to unmet demand

Something like this:
queue.png
queue.png (53.36 KiB) Viewed 4396 times
In queuing theory there's also the concept of "balking" where arrivals decline to joint the queue, because they immediately perceive that the line is too long.
by tomfid
Tue May 06, 2025 3:47 pm
Forum: Vensim
Topic: Tracking stock attributes
Replies: 3
Views: 4470

Re: Tracking stock attributes

I think the best option is to disaggregate the capacity stock into incentivized and older components. For example: capacity credit stock disagg.png There are two versions here. The top copy uses a standard first-order outflow on the stock of new incentive-eligible capacity. That may be appropriate f...
by tomfid
Tue May 06, 2025 3:22 pm
Forum: Vensim
Topic: Tracking stock attributes
Replies: 3
Views: 4470

Tracking stock attributes

Reposting a question from metasd.com: How do I add a variable that tracks the “age of a stock”? I am looking at an energy system dynamics model where tax incentives are offered for the first 10 years of an installed capacity operation. I have stock representing the installed capacity but need to set...
by tomfid
Mon May 05, 2025 3:43 pm
Forum: Vensim
Topic: "Sensitivity2All" for selected constants only
Replies: 3
Views: 6869

Re: "Sensitivity2All" for selected constants only

On the Advanced tab of the sens2all setup dialog, you can specify a savelist that excludes nuisance parameters:
sens2all exclude.png
sens2all exclude.png (120.18 KiB) Viewed 6857 times