Search found 3229 matches

by tomfid
Mon Apr 12, 2021 9:21 pm
Forum: Vensim
Topic: Best practice to avoid data warnings?
Replies: 4
Views: 78

Re: Best practice to avoid data warnings?

Thinking further about this, I would guess that many of the warnings are of the "starts before"/"ends after" type. It might make sense to have a global way to suppress those. Requiring explicit NA in the input data doesn't seem like a great solution - it would create a lot of clutter. What about hav...
by tomfid
Mon Apr 12, 2021 9:03 pm
Forum: Vensim
Topic: Auxiliary formulation for Annual profit
Replies: 1
Views: 38

Re: Auxiliary formulation for Annual profit

The PULSE approach is one way to do it, but I find it annoying because it creates a sawtooth that's hard to interpret, except at the annual endpoints. Another option is to integrate cash flow over a moving window. You can do that by creating a stock with an inflow of cash income and an outflow of ca...
by tomfid
Thu Apr 08, 2021 4:55 pm
Forum: Vensim
Topic: NPV for multiple investments
Replies: 3
Views: 112

Re: NPV for multiple investments

Yes, that would make sense.
by tomfid
Thu Apr 08, 2021 4:50 pm
Forum: Vensim
Topic: Best practice to avoid data warnings?
Replies: 4
Views: 78

Re: Best practice to avoid data warnings?

There isn't an explicit formalism for reading an NA in the input and therefore suppressing warnings as intentionally missing data, but that would be a useful addition. However, there is a way to suppress these warnings with .cin files, using :NODATA and some related statements. https://vensim.com/do...
by tomfid
Thu Apr 08, 2021 2:49 pm
Forum: Vensim
Topic: Delay vs Smooth
Replies: 1
Views: 60

Re: Delay vs Smooth

They differ if the time constant changes during the simulation.
by tomfid
Tue Apr 06, 2021 4:35 pm
Forum: Vensim
Topic: Set of initial values for a level with subscripts
Replies: 3
Views: 82

Re: Set of initial values for a level with subscripts

Also, for things that are not expressible as a list of constants, TABBED ARRAY, or GET XLS link, you can always write equations individually for each element of a subscript range:
https://vensim.com/documentation/21265.html
https://vensim.com/documentation/except ... tions.html
by tomfid
Mon Apr 05, 2021 5:32 pm
Forum: Vensim
Topic: NPV for multiple investments
Replies: 3
Views: 112

Re: NPV for multiple investments

Not sure how it happened, but somehow your calculated NPV equation has a null type. Set it to "auxiliary" and it will work.
by tomfid
Mon Apr 05, 2021 5:24 pm
Forum: Vensim
Topic: changing optimization models to SD models
Replies: 2
Views: 64

Re: changing optimization models to SD models

You could express this more or less directly in Vensim, and use the optimizer with U as the primary payoff, and a penalty term on noncompliance with the constraint.

However, this doesn't seem to have any dynamics of interest, so I don't see any advantage to using Vensim over any other tool.
by tomfid
Tue Mar 30, 2021 4:02 am
Forum: Vensim
Topic: PRO 8.2.1 questions
Replies: 4
Views: 102

Re: PRO 8.2.1 questions

I think they must have made some unusual choices when publishing these models. The Publish dialog allows you to select whether PLE/PLP, Pro, DSS etc. can open these individually. The first one, for example, won't open at all into DSS. The settings for PLE and PLE+ are linked, so you should still be ...
by tomfid
Tue Mar 23, 2021 3:44 am
Forum: Vensim
Topic: Issue with publishing to web
Replies: 11
Views: 244

Re: Issue with publishing to web

Also, be sure you're running the latest Vensim - one of the 8.1.x versions was mismatched with an emscripten update as I recall.
by tomfid
Mon Mar 22, 2021 8:34 pm
Forum: Vensim
Topic: Spreading subscript elements over time
Replies: 4
Views: 180

Re: Spreading subscript elements over time

Both will be supported for the foreseeable future. They have different strengths. If you have data with a sparse or ad hoc key structure, or you need dynamic creation/deletion of entities, Ventity makes a lot of sense. But Vensim has some unique capabilities as well, including richer optimization op...
by tomfid
Wed Mar 17, 2021 2:35 pm
Forum: Vensim
Topic: Subscript Selection and loaded VDFX resetting on model re-open
Replies: 4
Views: 157

Re: Subscript Selection and loaded VDFX resetting on model re-open

Also, CMD scripts when run from Vensim can load MDL files. I think the compile time is the problem here. Definitely check Model>Settings>File Format>Store settings in separate file. It should work, but if the settings are lost there could be a loose end in loading from scripts. Also, if you keep se...
by tomfid
Wed Mar 17, 2021 12:18 am
Forum: Vensim
Topic: Dairy supply chain help
Replies: 1
Views: 133

Re: Dairy supply chain help

I'd start by searching the SD conference archives for similar work.
by tomfid
Mon Mar 15, 2021 6:20 pm
Forum: Vensim
Topic: I'm having the following problem
Replies: 2
Views: 175

Re: I'm having the following problem

There's also an LP_solve link in an external function library: https://vensim.com/workbench/#lp-solve-link It would probably have to be recompiled for the latest version of Vensim.

Some problems can be solved by using FIND ZERO on the Lagrangian shadow price of the constraint.
by tomfid
Mon Mar 15, 2021 6:14 pm
Forum: Vensim
Topic: I'm having the following problem
Replies: 2
Views: 175

Re: I'm having the following problem

Generally such formulations are not a realistic model of behavior, though they are sometimes useful.

You can use the optimizer to solve the problem. https://www.vensim.com/documentation/21330.html
by tomfid
Mon Mar 15, 2021 2:12 am
Forum: Vensim
Topic: Controller
Replies: 10
Views: 473

Re: Controller

No, you don't really have to check it at all - it's just for verification that you've implemented the equations correctly.
by tomfid
Thu Mar 11, 2021 5:11 pm
Forum: Vensim
Topic: Controller
Replies: 10
Views: 473

Re: Controller

You can also call a, b and c weights. a = 100 b = 100 c = 100 sum of a b and c = a + b + c relative a = a / sum of a b and c relative b = b / sum of a b and c relative c = c / sum of a b and c check = relative a + relative b + relative c (this should be = 1) thx what do you mean by check? how the m...
by tomfid
Tue Mar 09, 2021 4:19 pm
Forum: Ventity
Topic: Accumulating stocks for calculations during a process list action
Replies: 6
Views: 305

Re: Accumulating stocks for calculations during a process list action

Emailed you a link to the nightly build that fixes this.
by tomfid
Mon Mar 08, 2021 9:10 pm
Forum: System Dynamics Discussion
Topic: QGIS - Phyton - Vensim
Replies: 8
Views: 3281

Re: QGIS - Phyton - Vensim

This forum is basically an archive, so I would ask the question elsewhere. Ventity may be a more natural fit - it has some native ability to display maps, and its data model is pretty close to a shapefile's attribute table.
by tomfid
Mon Mar 08, 2021 4:53 pm
Forum: Vensim
Topic: Vensim PLE 8.2.1 takes up to a minute to open on Mac Boot Camp
Replies: 2
Views: 226

Re: Vensim PLE 8.2.1 takes up to a minute to open on Mac Boot Camp

This sounds like something that happens when antivirus checks block opening, with some delay due to network or server latency. Any chance of that?
by tomfid
Mon Mar 08, 2021 4:46 pm
Forum: Ventity
Topic: Accumulating stocks for calculations during a process list action
Replies: 6
Views: 305

Re: Accumulating stocks for calculations during a process list action

Apparently a recent optimization of the process list created a bug in the sequencing of updates, so the mass stock is out of date, except when used in the "while" field. There's probably a workaround using a different configuration of internal stocks in the action, or I can send you a nightly build ...
by tomfid
Fri Mar 05, 2021 5:14 pm
Forum: Ventity
Topic: Accumulating stocks for calculations during a process list action
Replies: 6
Views: 305

Re: Accumulating stocks for calculations during a process list action

One option would be to give the cows an additional attribute "dead or alive" or perhaps a stock of "death date". Then the uneaten portion could simply be left in the cow in the pasture, with (potentially) more than one lion feeding on it, until the remainder was too old to eat. It's true that intern...
by tomfid
Fri Mar 05, 2021 4:27 pm
Forum: Ventity
Topic: Accumulating stocks for calculations during a process list action
Replies: 6
Views: 305

Re: Accumulating stocks for calculations during a process list action

Sounds delicious.

I'll take a look - there should be a way to do it.
by tomfid
Wed Mar 03, 2021 9:41 pm
Forum: Vensim
Topic: Vensim introducing backslashes in Var names before each underbar. Bug?
Replies: 6
Views: 283

Re: Vensim introducing backslashes in Var names before each underbar. Bug?

I'd completely forgotten about it, but there's one more setting to check:
2021-03-03_14-38-35.png
2021-03-03_14-38-35.png (8.49 KiB) Viewed 219 times
This might explain why you only have trouble with the one model.
by tomfid
Mon Mar 01, 2021 2:23 pm
Forum: Vensim
Topic: Vensim introducing backslashes in Var names before each underbar. Bug?
Replies: 6
Views: 283

Re: Vensim introducing backslashes in Var names before each underbar. Bug?

A few: - If you look at it with a text editor, does the troublesome model start with {UTF-8} consistently? Mixing pre- and post-unicode versions of Vensim could be an issue. - Try a Model>Reform & Clean before you start editing to see if the problem goes away (but be cautious before checking in, as ...