Search found 2960 matches

by tomfid
Thu Oct 14, 2010 6:27 pm
Forum: Vensim
Topic: vdf files - vensim dll
Replies: 5
Views: 2452

Here's one option: you can open a vdf as a model (via File>Open... - just change the file type setting). That let's you see the variables in the vdf - use the Variables tab of the control panel. You can then use the sketch tools to put the variables on a diagram and create a .mdl format data model f...
by tomfid
Tue Oct 05, 2010 3:42 pm
Forum: Vensim
Topic: Unit Error: Mantissa of ^ must be dimensionless
Replies: 3
Views: 1589

Sometimes, for transparency, it's good to take Bob's equation and break it out into several, for example:

output = reference output * effect of factor 1 * effect of factor 2
effect of factor 1 = (input 1/reference input 1)^factor 1
effect of factor 2 = (input 2/reference input 2)^factor 2
by tomfid
Tue Oct 05, 2010 3:39 pm
Forum: Vensim
Topic: Vensim for Dummies?
Replies: 15
Views: 5042

I typically add a units conversion variable to my model, so that I don't mix up % and fractions. For example: "100 percent" == 100 ~percent ~this is the conversion factor for percentages, with units of percent; note the == makes it an unchangeable constant unemployment rate = 3.5 ~percent ~a typical...
by tomfid
Tue Sep 28, 2010 4:43 pm
Forum: Vensim
Topic: Venapp Questions
Replies: 11
Views: 2188

Is there a SPECIAL>LOADRUN| command on your screen that might be rearranging the runs?

You could try a MENU>LOAD_RUN right after your MENU>RUN or MENU>RUN1 to (a) see whether the new run gets loaded in the order expected and (b) reorder the runs and see if that fixes your color problem.

Tom
by tomfid
Sun Sep 26, 2010 10:56 pm
Forum: Vensim
Topic: Venapp Questions
Replies: 11
Views: 2188

1 & 2: The RUNNAME display and graph coloring are both tied to the order in which datasets are loaded. The default when you use the MENU>RUN command is to load new runs last, which should preserve stable coloring. MENU>RUN1 loads new datasets first - my guess is that you're using RUN1 and switching ...
by tomfid
Sat Sep 25, 2010 10:58 pm
Forum: Vensim
Topic: vensim link matlab
Replies: 74
Views: 22417

It looks like you have some stray single-quote marks in your code.
by tomfid
Sat Sep 25, 2010 10:56 pm
Forum: Vensim
Topic: interpreting custom graph
Replies: 2
Views: 1365

If you check the box between variables on the left side of the custom graph definition window you can force the variables to use the same scale. Ordinarily this is only done when units match, but as long as you're OK equating jobs and people it should be fine in this case.
by tomfid
Fri Sep 24, 2010 2:53 pm
Forum: System Dynamics Discussion
Topic: Different between Stella , Vensim and Powersim, need help
Replies: 19
Views: 17663

I think the first question is, what are you trying to do? Different tools may be more or less appropriate for certain tasks. What are you modeling? What questions are you trying to answer? What's the time horizon of the model? What level of detail is desired? Who will make decisions based on the inf...
by tomfid
Fri Sep 24, 2010 1:46 pm
Forum: Vensim
Topic: what is .VGD means?
Replies: 1
Views: 736

A vgd is a graph definition file. You can save/open these through the Graphs tab of the Control Panel, or any text editor.
by tomfid
Thu Sep 23, 2010 7:12 pm
Forum: Vensim
Topic: Simple Optimization
Replies: 6
Views: 1769

In general, it's a little odd to optimize (desired inventory-actual inventory), because it's possible that discrepancies could arise as a consequence of poor formulation of desired inventory. A more typical setup would be to describe explicit costs of having too much or too little inventory, then op...
by tomfid
Tue Sep 21, 2010 9:02 pm
Forum: Vensim
Topic: problem running simulations
Replies: 8
Views: 2425

I think that the warnings about "not used..." are not the only errors ... scroll through the list of generated errors to see if there's anything else at the bottom (simultaneous equation problems will appear at the end of the list, for example).

Can you post the model?
by tomfid
Mon Sep 20, 2010 11:00 pm
Forum: Vensim
Topic: Sensitivity analysis input
Replies: 10
Views: 2963

You can use a file containing an actual sample of input parameters, not just distributions. You specify the name of the file in the sensitivity control file. Take a look again at Chapter 10 of the reference manual, e.g. File (use a file to specify parameters), if selected, will use a file to determi...
by tomfid
Mon Sep 20, 2010 10:48 pm
Forum: Vensim
Topic: vensim PLE question
Replies: 3
Views: 905

As long as you're using Euler or Diff integration, you can also use SMOOTH(p,TIME STEP).

It's worth pondering why you want a discrete delayed value - generally people are using this to either calculate derivatives or run discrete time models, both of which have pitfalls.

Tom
by tomfid
Sun Sep 12, 2010 8:44 pm
Forum: Vensim
Topic: custom graph
Replies: 5
Views: 1743

You can change this globally by adjusting the Horizontal setting on the Scaling tab of the Control Panel.
by tomfid
Tue Sep 07, 2010 10:44 pm
Forum: Vensim
Topic: Export data to Excel or something similar
Replies: 9
Views: 3187

It's a little more complicated than that. Take a look at venext.c in your Vensim comp directory. Your function could be almost as simple as the COSINE function example, if you're only writing one variable to a static output file. You'd still have to add some logic to open & close the file in simulat...
by tomfid
Tue Sep 07, 2010 6:08 pm
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

Why not do this in GAMS? With undefined units and no dynamics (except maybe the "delayed" variable, which isn't used in the sample), it seems like you're not taking advantage of Vensim's strengths.

Tom
by tomfid
Tue Sep 07, 2010 6:02 pm
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

Why not do this in GAMS? With undefined units and no dynamics (except maybe the "delayed" variable, which isn't used in the sample), it seems like you're not taking advantage of Vensim's strengths.

Tom
by tomfid
Tue Sep 07, 2010 1:00 pm
Forum: Vensim
Topic: Using Discrete Distributions in Sensitivity Analysis
Replies: 5
Views: 1225

Use INTEGER(x*10+0.5)/10
by tomfid
Tue Sep 07, 2010 2:16 am
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

Also, when you look a the solution at the initial time step, is it reasonable?
by tomfid
Tue Sep 07, 2010 2:15 am
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

Is this some kind of general equilibrium model? Some insight into the problem statement might help intuition about the solution. What is the origin of the time-varying behavior? Is it only the changing population? One possible reason that you don't have any units errors reported is that you haven't ...
by tomfid
Mon Sep 06, 2010 10:56 pm
Forum: Vensim
Topic: Export data to Excel or something similar
Replies: 9
Views: 3187

I think you'd have to write an external function to write the data to text. Fairly simple, but a lot of overhead to get started.

Tom
by tomfid
Mon Sep 06, 2010 9:29 pm
Forum: Vensim
Topic: Using Discrete Distributions in Sensitivity Analysis
Replies: 5
Views: 1225

INIT = INITIAL

INITIAL always has to appear first in an equation. I sometimes add an INIT macro to my models, so that I can write things like relativeX = x/INIT(x)

:MACRO: INIT(x)
INIT = INITIAL(x)
~ x
~ |

:END OF MACRO:
by tomfid
Sat Sep 04, 2010 1:11 am
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

No problem, I'll answer to Bob. Unfortunately I don't have a copy of Matlab these days, and I've never connected it to Vensim. When you say you were not able to continue for more than 5 time steps with Vensim, what was the problem? Did the model crash, or was it simply too slow, or ... ? Vensim's FI...
by tomfid
Fri Sep 03, 2010 8:10 pm
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

Your path C:\Vensimfloder\models\sample\ would be OK in XP - I don't know about Win7. But is it spelled Vensimfloder or Vensimfolder? You may have a typo.

Also, it appears that you have an extra ' in your model path, just before testlink: C:\Vensimfloder\models\sample\'testlink.vpm
by tomfid
Fri Sep 03, 2010 8:07 pm
Forum: Vensim
Topic: Call vensim
Replies: 91
Views: 25667

Out of curiousity, what are you trying to do here, i.e. what is the modeling purpose of calling Vensim from Matlab?