Search found 2776 matches

by tomfid
Fri Oct 18, 2019 4:00 pm
Forum: Vensim
Topic: synthesim (sim setup) in Vensim reader vs PLE vs DSS
Replies: 1
Views: 81

Re: synthesim (sim setup) in Vensim reader vs PLE vs DSS

The reader and DSS provide some additional features, like overrides and .cin file handling.

https://vensim.com/running-models-with- ... el-reader/
by tomfid
Fri Oct 18, 2019 3:57 pm
Forum: Vensim
Topic: Forecast or What?
Replies: 2
Views: 108

Re: Forecast or What?

The FORECAST function is just trend-extrapolation, which is sometimes useful but often pretty dumb. A more sophisticated approach would be to build a model that captures the driving forces for production, and fit the model to this data (by hand or by optimization). Then the model generates the forec...
by tomfid
Thu Oct 17, 2019 5:50 pm
Forum: Vensim
Topic: Subscript Subrange
Replies: 5
Views: 164

Re: Subscript Subrange

You can definitely use subranges for this. https://www.vensim.com/documentation/22100.htm I find it easiest to build them up hierarchically. For example: single : (single1-single50) twin : (twin1-twin50) aircraft : single, twin Then you can write distinct equations for maintenance[single] and mainte...
by tomfid
Thu Oct 17, 2019 4:49 pm
Forum: Vensim
Topic: Error in "GET XLS DATA" when I run a model that previously worked fine
Replies: 6
Views: 182

Re: Error in "GET XLS DATA" when I run a model that previously worked fine

You can switch to text view (View>As Text) and use the search & replace (Edit>Replace String). Or, save the model to mdl and use your favorite text editor (Notepad++ is good and free).
by tomfid
Thu Oct 17, 2019 2:15 am
Forum: Vensim
Topic: Error in "GET XLS DATA" when I run a model that previously worked fine
Replies: 6
Views: 182

Re: Error in "GET XLS DATA" when I run a model that previously worked fine

I've had the same problem recently on 1 out of 3 systems. I think it may be an Excel change. Switching from GET XLS to GET DIRECT may help.
by tomfid
Wed Oct 16, 2019 6:19 pm
Forum: Vensim
Topic: Problem with Command Script using GET XLS CONSTANTS
Replies: 12
Views: 244

Re: Problem with Command Script using GET XLS CONSTANTS

How many datasets do you have? You could create a data variable for each, then switch the data used numerically, rather than switching the source name. It's a little inefficient, but it won't matter unless the dataset is large.
by tomfid
Wed Oct 16, 2019 4:19 pm
Forum: Ventity
Topic: Published Research using Ventity
Replies: 4
Views: 230

Re: Published Research using Ventity

Cool. I can't see through the paywall - is this a hybrid, with CLDs in Vensim and the model in Ventity?
by tomfid
Wed Oct 16, 2019 4:05 am
Forum: Vensim
Topic: How to specify a vector of data in Vensim P.L.E. 8.0.4. x64
Replies: 4
Views: 151

Re: How to specify a vector of data in Vensim P.L.E. 8.0.4. x64

I should add that Ventity has detail and data capability, and is currently free for academic use.
by tomfid
Tue Oct 15, 2019 2:27 pm
Forum: Vensim
Topic: Improving the modelling of annual decisions used for optimization
Replies: 6
Views: 208

Re: Improving the modelling of annual decisions used for optimization

Generally, yes. VECTOR LOOKUP is potentially better because it interpolates, so you could have fewer points than there are time steps in the model.

A feedback-based decision rule is still superior.
by tomfid
Mon Oct 14, 2019 6:35 pm
Forum: Vensim
Topic: The question about Find Zero function
Replies: 5
Views: 147

Re: The question about Find Zero function

I don't know what any of this means, but with a corrected expression it works:
FIND ZERO 2.mdl
(9.73 KiB) Downloaded 12 times
by tomfid
Mon Oct 14, 2019 6:25 pm
Forum: Ventity
Topic: Published Research using Ventity
Replies: 4
Views: 230

Re: Published Research using Ventity

There isn't too much yet, due to the lags in adoption and publication, but if you point us to something, we'd be happy to feature it, and perhaps to start a page on the Ventity site.
by tomfid
Mon Oct 14, 2019 5:34 pm
Forum: Vensim
Topic: The question about Find Zero function
Replies: 5
Views: 147

Re: The question about Find Zero function

To clarify, the equation in the model uploaded appears to differ from the one in your initial post. The model has no solution; the original equation might.
by tomfid
Mon Oct 14, 2019 5:24 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 35
Views: 1407

Re: sensitivity analysis (vensim)

We're working on it, but I'm not sure whether it'll be done by end of year. The speedup is more than noticeable if you have a many-core machine. Older workstations with 16 or more cores are now readily available at dirt cheap prices. We'll keep you posted as this evolves.
by tomfid
Mon Oct 14, 2019 5:21 pm
Forum: Vensim
Topic: The question about Find Zero function
Replies: 5
Views: 147

Re: The question about Find Zero function

I think the immediate problem is that you have the initial guess (initial x) set to 0. If the function's first execution is invalid, it can't proceed with a search.

If you set initial x = 1, it runs, but there's no solution to the equation, so it still fails to converge.
by tomfid
Mon Oct 14, 2019 4:00 pm
Forum: Vensim
Topic: Improving the modelling of annual decisions used for optimization
Replies: 6
Views: 208

Re: Improving the modelling of annual decisions used for optimization

You need to specify the subscript dimension:
0<=timevalues[timerange]<=150
by tomfid
Mon Oct 14, 2019 2:52 pm
Forum: Vensim
Topic: Noise Seed in Venapp
Replies: 4
Views: 141

Re: Noise Seed in Venapp

Hossein is correct - the sensitivity seed can't be changed programmatically. We should change that. A workaround is to provide several different vsc files with different seeds. Another possibility is to use the vsc file to vary noise seed, and generate the distributions for the target variables insi...
by tomfid
Fri Oct 11, 2019 12:42 pm
Forum: Vensim
Topic: Noise Seed in Venapp
Replies: 4
Views: 141

Re: Noise Seed in Venapp

Add NOISE SEED to the model and change it with SETVAL.
https://www.vensim.com/documentation/noise_seed.htm
by tomfid
Thu Oct 10, 2019 4:52 pm
Forum: Vensim
Topic: How to specify a vector of data in Vensim P.L.E. 8.0.4. x64
Replies: 4
Views: 151

Re: How to specify a vector of data in Vensim P.L.E. 8.0.4. x64

Correct. Arrays are a Pro/DSS feature only.

PLE is really focused on learning about dynamics - it doesn't do detail complexity and data.

If you email us, we'd be happy to send you an evaluation license for Pro/DSS for testing.
by tomfid
Thu Oct 10, 2019 1:46 pm
Forum: Vensim
Topic: Giving time series data
Replies: 12
Views: 1182

Re: Giving time series data

Are you talking about the units or granularity of the data? Generally it's always better to use the finest time scale you can, given the time step of the model.
by tomfid
Wed Oct 09, 2019 7:23 pm
Forum: Vensim
Topic: Negative Levels
Replies: 6
Views: 150

Re: Negative Levels

This is puzzling ... we've never dropped Euler's method, and there haven't been any changes to the sim engine in v8. If you have a model demonstrating the problem, or a screenshot, we'd be very interested to explore the issue.
by tomfid
Wed Oct 09, 2019 5:22 pm
Forum: Vensim
Topic: Giving time series data
Replies: 12
Views: 1182

Re: Giving time series data

Vensim will be looking for time formatted as a decimal year.
by tomfid
Wed Oct 09, 2019 1:32 pm
Forum: Vensim
Topic: Problem with Command Script using GET XLS CONSTANTS
Replies: 12
Views: 244

Re: Problem with Command Script using GET XLS CONSTANTS

The .cin file trick also fails.
by tomfid
Wed Oct 09, 2019 1:28 pm
Forum: Vensim
Topic: Problem with Command Script using GET XLS CONSTANTS
Replies: 12
Views: 244

Re: Problem with Command Script using GET XLS CONSTANTS

Note the provision in the docs for SETVAL: If you are using the SETVAL command to set a string variable do not include the surrounding single quotes. For example: SIMULATE>SETVAL|productname:IS:Metronone However, that alone is not sufficient to resolve the problem - it still seems to fail silently.
by tomfid
Fri Oct 04, 2019 3:23 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 35
Views: 1407

Re: sensitivity analysis (vensim)

There's a little advice on speed here: https://metasd.com/2011/01/optimizing-vensim-models/ One item that's not mentioned there is that restricting the savelist helps. We have an experimental version that does parallel multicore execution, which would reduce your simulation time by a factor of the n...