Search found 3800 matches

by tomfid
Fri May 04, 2012 2:41 pm
Forum: Vensim
Topic: problem moving around the arrows on a model's sketch
Replies: 2
Views: 1875

Re: problem moving around the arrows on a model's sketch

I think the first issue occurs because the big view is scaled to fit the screen, while the others are at 100%. So, regrettably, there probably isn't a way to get the arrowheads to match. The second is probably also exacerbated by scaling, but clearly it would help if we made the hot spot for arrow h...
by tomfid
Fri May 04, 2012 2:11 pm
Forum: Vensim
Topic: What improvements would you like to see in Vensim?
Replies: 150
Views: 10429855

Keep the ideas coming!

Some of these things will take a while, but we're listening.
by tomfid
Mon Apr 23, 2012 11:27 pm
Forum: Vensim
Topic: Can Vensim work with 64 Bit Excel?
Replies: 3
Views: 3361

Re: Can Vensim work with 64 Bit Excel?

The other open question is whether you can call the (32 bit) dll from a VB script in a 64 bit app. Some 32/64 mixed environments don't work - for example, you can't call a 32 bit JNI dll from a 64 bit virtual machine in Java.

Tom
by tomfid
Thu Apr 19, 2012 2:42 pm
Forum: Vensim
Topic: Annualizing 6 month output
Replies: 4
Views: 3904

Re: Annualizing 6 month output

The answer partly depends on whether your model has units of years, with time step = 0.5, or months with time step = 6. If you're running in years, flows already have instantaneous annualized values, so you don't need to do anything unless you need to capture the actual reporting lag involved in ann...
by tomfid
Fri Apr 13, 2012 1:36 pm
Forum: Vensim
Topic: What does this error message mean?
Replies: 5
Views: 5440

Re: What does this error message mean?

We're working on it.

I don't think it'll help with memory, but if your arrays are sparse, VECTOR SELECT can help quite a bit with execution time.
by tomfid
Fri Apr 13, 2012 1:35 pm
Forum: Vensim
Topic: Equation editor hangs programme
Replies: 19
Views: 14955

Re: Equation editor hangs programme

Not sure why this is happening. The error files are unfortunately uninformative (at least to me). What operating system version are you using? One thing to try would be simply deleting (or renaming) the vensim.ini file mentioned in Tony's March 4 post (Vensim should recreate a fresh one on startup)....
by tomfid
Thu Apr 12, 2012 11:30 pm
Forum: Vensim
Topic: Confusing error
Replies: 1
Views: 1578

Re: Confusing error

This error is generated when you're using all the elements of an array, but not computing some of them. For example: myrange : mysubA, mysubB mysubA : (sa1-sa10) mysubB : (sb1-sb10) datavar[mysubA] := GET XLS DATA( ... ) auxvar[myrange] = 3*datavar[myrange] Notice that above, datavar is used with [m...
by tomfid
Thu Apr 12, 2012 11:26 pm
Forum: Vensim
Topic: What does this error message mean?
Replies: 5
Views: 5440

Re: What does this error message mean?

You may be limited by your largest array block - what number does it give with the "insufficient memory" error? (I'm guessing somewhere upward of 500 megabytes)
by tomfid
Wed Apr 11, 2012 8:12 pm
Forum: Vensim
Topic: What does this error message mean?
Replies: 5
Views: 5440

Re: What does this error message mean?

When does it happen?

It could be that your model is too big to be executed. Check Model>Settings>Info and see how many equations there are.

Tom
by tomfid
Tue Apr 10, 2012 5:02 pm
Forum: Vensim
Topic: Equation editor hangs programme
Replies: 19
Views: 14955

Re: Equation editor hangs programme

Is there a particular model that offends, that you can post?
by tomfid
Tue Apr 03, 2012 2:46 am
Forum: Vensim
Topic: Insufficient memory in Vensim
Replies: 6
Views: 3908

Re: Insufficient memory in Vensim

194k should not be a problem - it might be a little slow, but not terrible - unless your time range is very large. For example, if your (FINAL TIME-INITIAL TIME)/TIME STEP is much greater than 10,000 that might be an issue. However, if the info says, "cannot be simulated," you have a synta...
by tomfid
Mon Apr 02, 2012 9:16 pm
Forum: Vensim
Topic: Insufficient memory in Vensim
Replies: 6
Views: 3908

Re: Insufficient memory in Vensim

Do you mean ranges with 3 elements (like city : boston, denver, chicago ) or variables with 3 ranges (like price[commodity,city,flavor])? If it's the latter, your model may be very large. A variable with 6 ranges will have N^6 elements, where N is the dimension of each range. If N=10, for example, y...
by tomfid
Mon Apr 02, 2012 8:05 pm
Forum: Vensim
Topic: moving backward in games with delays
Replies: 2
Views: 1864

Re: moving backward in games with delays

Noted. Thanks!

I haven't tried it, but it might be possible to store the decisions from a game in a .gin file, and then restart from the beginning and run up to the desired point using the .gin. Computationally wastefull, but maybe OK?
by tomfid
Tue Mar 27, 2012 9:29 pm
Forum: Vensim
Topic: Over Allocation
Replies: 4
Views: 4095

Re: Over Allocation

This kind of problem can be pretty messy (which is why it takes an iterative solver, as in Excel). It would be very natural to solve as a linear program. Mechanically, your model has 2 issues, fixed below. First, you're feeding in [problem,collect] tasks at the left, where it should probably be just...
by tomfid
Tue Mar 27, 2012 2:56 pm
Forum: Vensim
Topic: Over Allocation
Replies: 4
Views: 4095

Re: Over Allocation

Have you checked the example in the Help system, Ch. 4, Reference Manual, functions?

ALLOCATE AVAILABLE isn't designed for many-to-many situations (Relays -> Collects) so the behavior you're getting sounds right. I think we need to debug your FIND MARKET PRICE version.
by tomfid
Mon Mar 26, 2012 5:57 pm
Forum: Vensim
Topic: Kernel density estimation
Replies: 8
Views: 4095

Re: Kernel density estimation

OK. I think my example should work for you.
by tomfid
Mon Mar 26, 2012 4:34 pm
Forum: Vensim
Topic: Kernel density estimation
Replies: 8
Views: 4095

Re: Kernel density estimation

Here's an example:
kernel density.mdl
(3.7 KiB) Downloaded 216 times
I haven't double checked to be sure that the resulting pdf integrates to 1, but it should be OK.
by tomfid
Mon Mar 26, 2012 3:34 pm
Forum: Vensim
Topic: Kernel density estimation
Replies: 8
Views: 4095

Re: Kernel density estimation

OK - I think this is actually fairly easy. I'll post an example. One more question though: once you have the kernel-smoothed density, what will you do with it? For example, do you want to pick arbitrary points from it, or generate incomes at uniformly-spaced levels, essentially using the pdf as an i...
by tomfid
Mon Mar 26, 2012 1:29 pm
Forum: Vensim
Topic: error messages related to lookups
Replies: 10
Views: 10856

Re: error messages related to lookups

Specifically, see:

http://www.vensim.com/documentation/fn_lookup_area.htm

There's a chapter in the User's Guide on lookups:

http://www.vensim.com/documentation/usr08.htm

For iThink users, the WITH LOOKUP syntax may be more familiar:

http://www.vensim.com/documentation/fn_with_lookup.htm
by tomfid
Sun Mar 25, 2012 6:19 pm
Forum: Vensim
Topic: how to perform a convolution in vensim
Replies: 17
Views: 12403

Re: how to perform a convolution in vensim

It's using the profile and the delay time together to normalize the pdf and establish the mean time. Off the top of my head, I believe that the procedure is (a) integrate x*lookup(x) over the range of the lookup, and divide by the range, to determine the mean arrival time in the lookup (b) rescale t...
by tomfid
Sun Mar 25, 2012 2:18 am
Forum: Vensim
Topic: error messages related to lookups
Replies: 10
Views: 10856

Re: error messages related to lookups

Vensim differs from iThink in that a lookup can be used in more than one place, so the lookup table is separate from the input and expressions that use the input. In that respect it is more like DYNAMO. In DYNAMO you might write: FCAOR = TABHL( FCAORT, NRFR, 0, 1, .1 ) FCAORT = 1/.9/.7/.5 ... (borro...
by tomfid
Sat Mar 24, 2012 5:26 pm
Forum: Vensim
Topic: how to perform a convolution in vensim
Replies: 17
Views: 12403

Re: how to perform a convolution in vensim

Incidentally, if there's some other software you use that does things differently/better, we're always interested to hear about it.
by tomfid
Sat Mar 24, 2012 5:25 pm
Forum: Vensim
Topic: how to perform a convolution in vensim
Replies: 17
Views: 12403

Re: how to perform a convolution in vensim

I'll take a look. If you don't need 'init' and 'init grow' you can set them to 0. The profile and delay time parameters work together. The profile gives the shape of the distribution. It's then scaled so that (a) the area under the curve is 1 and (b) the mean arrival time is equal to the delay time ...
by tomfid
Sat Mar 24, 2012 4:28 pm
Forum: Vensim
Topic: Kernel density estimation
Replies: 8
Views: 4095

Re: Kernel density estimation

Are you trying to smooth across time, or income values, or both?

If this is all you're doing, you'd be better off using a stats package. But if this is part of a dynamic model, we can probably come up with a strategy that works.

Tom