Search found 3999 matches

by tomfid
Fri Jun 20, 2025 8:36 pm
Forum: Vensim
Topic: Non-integer Poisson Warning
Replies: 2
Views: 85

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: 164

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: 164

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: 367

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: 1420

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: 2226

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: 2595

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: 2595

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: 4408

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: 2318

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: 3736

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: 2905

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: 3416

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: 4199

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: 4116

Re: How to model delayed flows due to unmet demand

Something like this:
queue.png
queue.png (53.36 KiB) Viewed 4086 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: 4199

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: 4199

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: 6120

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 6108 times
by tomfid
Mon May 05, 2025 3:39 pm
Forum: Vensim
Topic: Lookups in new equation editor
Replies: 5
Views: 5844

Re: Lookups in new equation editor

Note that the [+] button becomes visible after you make the initial family selection:
sub plus.png
sub plus.png (22.45 KiB) Viewed 5664 times
by tomfid
Mon May 05, 2025 3:35 pm
Forum: Vensim
Topic: Lookups in new equation editor
Replies: 5
Views: 5844

Re: Lookups in new equation editor

It's a two-tier process. First (and only once), set the family associated with the equation: sub families.png Then, if you need distinct equations for subranges or specific elements, right-click the tab or use the dropdown on the Subscripts button to set those: sub elements.png sub element 2.png
by tomfid
Sat May 03, 2025 1:44 pm
Forum: Vensim
Topic: Lookups in new equation editor
Replies: 5
Views: 5844

Re: Lookups in new equation editor

It works - example: subscript 2025-05-03_07-37-19.png Procedure: Click the Subscripts button the first time you add ranges to set the relevant families Use the [+] button to add a tab if you need an additional element Right-click the new tab to set Subranges and Elements (and Exceptions if any) ... ...
by tomfid
Mon Apr 28, 2025 1:05 pm
Forum: Vensim
Topic: Vensim: How to I add value annually
Replies: 4
Views: 4655

Re: Vensim: How to I add value annually

Putting PULSE TRAIN in the Initial Value field, as in your second example, won't work because the initial value doesn't change - it just initializes the stock. In your first example, if "Input" is constant at 1.1M and "Recycled Plastic & Monomer Feedstock" is constant, that m...
by tomfid
Wed Apr 02, 2025 6:21 pm
Forum: Vensim
Topic: insert picture into Aux / Stock variable?
Replies: 8
Views: 9161

Re: insert picture into Aux / Stock variable?

Funny. I think there's probably a font that would make those unicode chars cross-platform, but it wasn't obvious which one. The model runs though.
by tomfid
Wed Apr 02, 2025 3:55 pm
Forum: Vensim
Topic: Watermark model output?
Replies: 3
Views: 2772

Re: Watermark model output?

I think you can specify page header/footer info if you print to PDF?
by tomfid
Wed Apr 02, 2025 2:55 pm
Forum: Vensim
Topic: identifying contributors to large file size and slow run time
Replies: 16
Views: 14865

Re: identifying contributors to large file size and slow run time

For file size, the most likely candidate is heavily-subscripted variables. We don't have a way to identify these built in, but here's a trick: - export a run to a tab or csv file, with subscripts in their own columns - to minimize the file size, you can set the time range to capture just the first 2...