Search found 3806 matches
- Thu Mar 28, 2024 6:17 pm
- Forum: Vensim
- Topic: double-click selection
- Replies: 5
- Views: 115
Re: double-click selection
Some of this will change with the new equation editor soon.
- Thu Mar 28, 2024 6:16 pm
- Forum: Vensim
- Topic: How to calculate the difference in value for a variable in vensim over time?
- Replies: 2
- Views: 28
Re: How to calculate the difference in value for a variable in vensim over time?
You can use DELAY FIXED for this: Previous GDP = DELAY FIXED( Current GDP, one year, Current GDP ) ~ $/year one year == 1 ~ year In continuous time, you can use the SMOOTH function, i.e. Previous GDP = SMOOTH( Current GDP, one year ) ~ $/year You can also use the TREND function to compute a fraction...
- Thu Mar 21, 2024 1:11 am
- Forum: Vensim
- Topic: it is frustrating!
- Replies: 25
- Views: 564
Re: it is frustrating!
Is the run "current" the first loaded dataset?
- Thu Mar 21, 2024 1:10 am
- Forum: Vensim
- Topic: Continuos or discrete variables?
- Replies: 4
- Views: 94
Re: Continuos or discrete variables?
On the other hand, if you're interested in stochastic extinction of a disease in a small population, integer values may matter.
It's impossible to answer these questions in general; some specifics of the question to be answered must be known.
It's impossible to answer these questions in general; some specifics of the question to be answered must be known.
- Thu Mar 21, 2024 1:08 am
- Forum: Vensim
- Topic: Continuos or discrete variables?
- Replies: 4
- Views: 94
Re: Continuos or discrete variables?
Like Forrester, I think that discrete quantities are rarely a good place to start. Things that are theoretically only available in integer quantities either don't matter, or have qualifications. For example, people are certainly available in integer quantities. But what about the work-equivalent of ...
- Thu Mar 21, 2024 1:04 am
- Forum: Vensim
- Topic: Continuos or discrete variables?
- Replies: 4
- Views: 94
- Fri Mar 08, 2024 3:57 pm
- Forum: Vensim
- Topic: Help with PULSE TRAIN and random variable
- Replies: 6
- Views: 136
Re: Help with PULSE TRAIN and random variable
Try this instead ...
You can also use SAMPLE IF TRUE for this (though I think it's not available in all versions).
You can also use SAMPLE IF TRUE for this (though I think it's not available in all versions).
- Tue Mar 05, 2024 2:06 pm
- Forum: Vensim
- Topic: it is frustrating!
- Replies: 25
- Views: 564
- Mon Mar 04, 2024 4:36 pm
- Forum: Vensim
- Topic: where is the sim set up from the old GUI in the new one?
- Replies: 9
- Views: 10881
Re: where is the sim set up from the old GUI in the new one?
Not sure I'm tracking the issue here. In the old gui, PLE sim setup doesn't have a dialog. Everything is in the toolbar. 2024-03-04_09-33-54.png In the new gui, PLE does have a dialog (albeit without much content). 2024-03-04_09-32-44.png In both cases, constants and lookups are highlighted, and you...
- Mon Feb 05, 2024 11:10 pm
- Forum: Vensim
- Topic: Reinstall Vensim (error 977).
- Replies: 5
- Views: 562
Re: Reinstall Vensim (error 977).
Typically this indicates a path problem. Have you moved the dll?
- Fri Feb 02, 2024 4:00 pm
- Forum: Vensim
- Topic: RC Fonksiyon
- Replies: 1
- Views: 394
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
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
- 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: 939
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.
- Fri Feb 02, 2024 1:52 pm
- Forum: Vensim
- Topic: Can the Vensim PLE version achieve seasonal forecasting?
- Replies: 2
- Views: 531
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.
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.
- Thu Feb 01, 2024 3:45 pm
- Forum: Vensim
- Topic: Units tips or laws
- Replies: 7
- Views: 727
Re: Units tips or laws
Your flows are dimensioned dmnl/hour, but your time unit in Model>Settings is Mes.
- Wed Jan 31, 2024 3:57 pm
- Forum: Vensim
- Topic: Units tips or laws
- Replies: 7
- Views: 727
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...
- Mon Jan 29, 2024 6:30 pm
- Forum: Vensim
- Topic: Copy & Paste between models
- Replies: 4
- Views: 498
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.
In pro/DSS, general settings, you can enable opening multiple models simultaneously.
- Thu Jan 25, 2024 5:35 pm
- Forum: Vensim
- Topic: Max file size
- Replies: 5
- Views: 1067
Re: Max file size
I think the 3221226505 return code may be a variable type mismatch - this has been reported in other contexts.
- Sun Jan 14, 2024 11:19 pm
- Forum: Vensim
- Topic: Finding MAX of simulation variable
- Replies: 2
- Views: 937
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.
- Wed Jan 10, 2024 5:44 pm
- Forum: Vensim
- Topic: Get data xls with multiple subscripts
- Replies: 4
- Views: 3585
Re: Get data xls with multiple subscripts
In a case like this, importing the data to vdf would be less error-prone.
- Wed Jan 10, 2024 5:42 pm
- Forum: Vensim
- Topic: Get data xls with multiple subscripts
- Replies: 4
- Views: 3585
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.
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.
- Sat Jan 06, 2024 5:33 pm
- Forum: Vensim
- Topic: Vensim not correctly calculating stock from flows
- Replies: 4
- Views: 6574
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...
- Sat Jan 06, 2024 3:23 pm
- Forum: Vensim
- Topic: Vensim not correctly calculating stock from flows
- Replies: 4
- Views: 6574
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...
- Tue Jan 02, 2024 10:46 pm
- Forum: Vensim
- Topic: Solving for implicit functions before starting time
- Replies: 7
- Views: 9573
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...
- Fri Dec 29, 2023 4:02 pm
- Forum: Vensim
- Topic: Solving for implicit functions before starting time
- Replies: 7
- Views: 9573
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.
- Fri Dec 22, 2023 3:14 pm
- Forum: Vensim
- Topic: Can't view model as sketch
- Replies: 12
- Views: 11908
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.