Search found 3797 matches

by tomfid
Mon Feb 05, 2024 11:10 pm
Forum: Vensim
Topic: Reinstall Vensim (error 977).
Replies: 5
Views: 442

Re: Reinstall Vensim (error 977).

Typically this indicates a path problem. Have you moved the dll?
by tomfid
Fri Feb 02, 2024 4:00 pm
Forum: Vensim
Topic: RC Fonksiyon
Replies: 1
Views: 318

Re: RC Fonksiyon

I think you'll have to elaborate a bit, because there are a lot of different possible population structures, which might call for different approaches.

One option is to use the Little's Law equilibrium estimate, i.e. residence time = stock/flow_throughput. https://en.wikipedia.org/wiki/Little%27s_law
by tomfid
Fri Feb 02, 2024 2:00 pm
Forum: System Dynamics Discussion
Topic: Utilizing Ventana Systems Tools for enhancing data breach protection strategies ?
Replies: 3
Views: 799

Re: Utilizing Ventana Systems Tools for enhancing data breach protection strategies ?

For starters, google "sander zeijlemaker security system dynamics" - he's done quite a bit of interesting work. You should be able to find much of it in the ISDC conference proceedings.
by tomfid
Fri Feb 02, 2024 1:52 pm
Forum: Vensim
Topic: Can the Vensim PLE version achieve seasonal forecasting?
Replies: 2
Views: 447

Re: Can the Vensim PLE version achieve seasonal forecasting?

I think the month variable is intentional, for creating a seasonal input.

Since the seasonal behavior has 3 episodes, switched in an IF THEN ELSE statement, I think you could create the same thing for seasonal smoothing - have 3 smoothing structures, one active during each episode.
by tomfid
Thu Feb 01, 2024 3:45 pm
Forum: Vensim
Topic: Units tips or laws
Replies: 7
Views: 614

Re: Units tips or laws

Your flows are dimensioned dmnl/hour, but your time unit in Model>Settings is Mes.
by tomfid
Wed Jan 31, 2024 3:57 pm
Forum: Vensim
Topic: Units tips or laws
Replies: 7
Views: 614

Re: Units tips or laws

There are at least two rules: - a flow has the same units as the stock it connects to, divided by the time unit - EXP, LN, and a number of other functions require dimensionless units beyond that, if you have y = a / b the units follow y units = a units/b units One consequence of this is that you can...
by tomfid
Mon Jan 29, 2024 6:30 pm
Forum: Vensim
Topic: Copy & Paste between models
Replies: 1
Views: 386

Re: Copy & Paste between models

If you open them in the same application instance, this works. (If you open the files by double-clicking from the finder/explorer, you have two application instances, and it won't work.)

In pro/DSS, general settings, you can enable opening multiple models simultaneously.
by tomfid
Thu Jan 25, 2024 5:35 pm
Forum: Vensim
Topic: Max file size
Replies: 5
Views: 974

Re: Max file size

I think the 3221226505 return code may be a variable type mismatch - this has been reported in other contexts.
by tomfid
Sun Jan 14, 2024 11:19 pm
Forum: Vensim
Topic: Finding MAX of simulation variable
Replies: 2
Views: 769

Re: Finding MAX of simulation variable

If you can make the calculation at FINAL TIME, you can use SAMPLE IF TRUE to hold the max value over the simulation - there's an example in the help system.
by tomfid
Wed Jan 10, 2024 5:44 pm
Forum: Vensim
Topic: Get data xls with multiple subscripts
Replies: 4
Views: 2058

Re: Get data xls with multiple subscripts

In a case like this, importing the data to vdf would be less error-prone.
by tomfid
Wed Jan 10, 2024 5:42 pm
Forum: Vensim
Topic: Get data xls with multiple subscripts
Replies: 4
Views: 2058

Re: Get data xls with multiple subscripts

The GET DATA calls are basically 1-dimensional because the spreadsheet is 2D, and one is taken by time.

One possible way to semi-automate a GET call with more dimensions is to put the sheet names or first-cell references in a string variable with the appropriate subscripting.
by tomfid
Sat Jan 06, 2024 5:33 pm
Forum: Vensim
Topic: Vensim not correctly calculating stock from flows
Replies: 4
Views: 4410

Re: Vensim not correctly calculating stock from flows

Right. Personally I find it hard to remember the beginning/ending balance sequencing. It would be nice if we could update the table tool to make it easy to toggle display of stocks as start/end of period, though that might be tricky for some variables using functions like SAMPLE IF TRUE. It would al...
by tomfid
Sat Jan 06, 2024 3:23 pm
Forum: Vensim
Topic: Vensim not correctly calculating stock from flows
Replies: 4
Views: 4410

Re: Vensim not correctly calculating stock from flows

I think that the computation is actually correct. The Euler update in your spreadsheet is: stock(t + dt) = stock(t) + flows This is fine if the TIME STEP (dt) = 1, but in this model it's 0.25. The correct Euler update is: stock(t + dt) = stock(t) + flows*dt In this case, the value 1618 in cell F37 i...
by tomfid
Tue Jan 02, 2024 10:46 pm
Forum: Vensim
Topic: Solving for implicit functions before starting time
Replies: 7
Views: 6310

Re: Solving for implicit functions before starting time

I agree. The drawback of a lookup is that it might not be totally general (i.e. you'd have to recompute the values if some assumption changed). My guess is that the speed penalty for FIND ZERO is small. Unfortunately, you can't wrap FIND ZERO in an INITIAL statement, but you could set the error vect...
by tomfid
Fri Dec 29, 2023 4:02 pm
Forum: Vensim
Topic: Solving for implicit functions before starting time
Replies: 7
Views: 6310

Re: Solving for implicit functions before starting time

Another option would be to put a table of solutions (Moody diagram) into a lookup or fitted function.
by tomfid
Fri Dec 22, 2023 3:14 pm
Forum: Vensim
Topic: Can't view model as sketch
Replies: 12
Views: 9480

Re: Can't view model as sketch

This means there are syntax errors in the equations. Use Check Model <ctl><T> to see the error window.
by tomfid
Fri Dec 22, 2023 3:13 pm
Forum: Vensim
Topic: download stel2ven.zip and/or stel2ven.exe
Replies: 2
Views: 2940

Re: download stel2ven.zip and/or stel2ven.exe

Newer Stella models are in XMILE, which you can import via the File menu.
by tomfid
Fri Dec 22, 2023 3:12 pm
Forum: Vensim
Topic: Erased variables
Replies: 2
Views: 1614

Re: Erased variables

Whether variables remain in the model depends on user choice - when you delete a variable with the delete key, a dialog asks whether to remove them from the model or only the current view. You can find these variables by opening the Control Panel > Variables tab, and selecting the "orphans"...
by tomfid
Sat Dec 16, 2023 10:52 pm
Forum: Ventity
Topic: Very strange behavior when I edit auxiliary names
Replies: 1
Views: 5407

Re: Very strange behavior when I edit auxiliary names

I can replicate this. Ticketed for the devs to take a look.
by tomfid
Sat Dec 16, 2023 10:47 pm
Forum: Ventity
Topic: Ventity download
Replies: 1
Views: 3930

Re: Ventity download

It's working right now. There was an intermittent issue that seems to be resolved with our last web site update. Sorry for the issue.
by tomfid
Fri Dec 15, 2023 4:58 pm
Forum: Vensim
Topic: Sub-Subscripts?
Replies: 3
Views: 2177

Re: Sub-Subscripts?

Notice here that the COUNTRIES range is built up hierarchically by first defining euro and non-euro subranges. That's not necessary however - you can mix & match ranges and elements. City : Boston, Las Vegas, Denver, San Diego, Seattle, New York East Coast : Boston, New York West Coast : San Die...
by tomfid
Tue Dec 12, 2023 2:11 pm
Forum: Vensim
Topic: Level initial series
Replies: 4
Views: 2971

Re: Level initial series

It sounds like you want a population stock that's moving approximately alongside the data from 1995-2023, then reset the population stock to precisely match the data at 2023, then have the population evolve into the future by endogenous forces? If so, there are several ways to do this. The general i...
by tomfid
Tue Dec 12, 2023 2:01 pm
Forum: Vensim
Topic: Percent
Replies: 3
Views: 2854

Re: Percent

If the endpoint is fixed, you can use the approach of creating a variable.

If the endpoint is uncertain, specifically, not known at the start of the run, there isn't really a way to do this, except by postprocessing the output in some other tool (Excel, R, Python ...)
by tomfid
Wed Dec 06, 2023 3:35 pm
Forum: Vensim
Topic: Uniform data
Replies: 2
Views: 2579

Re: Uniform data

You can use these distributions either in equations, or via the sensitivity (Monte Carlo) tool.
by tomfid
Tue Dec 05, 2023 4:36 pm
Forum: Vensim
Topic: older interface PLE 10.1.3
Replies: 2
Views: 2456

Re: older interface PLE 10.1.3

Is there something specific that you need from the older interface?