Search found 3806 matches

by tomfid
Tue Feb 02, 2016 4:47 pm
Forum: Vensim
Topic: DelayN with leakage?
Replies: 6
Views: 3743

Re: DelayN with leakage?

It seems like a funny dataset - I wouldn't think people would have accurate perceptions of lifetimes for durable equipment. Plus, as you point out, their confidence bounds may be uncalibrated. Anyhow, I wouldn't think that a variable delay order between levels was desirable. Even if the leakage prob...
by tomfid
Mon Feb 01, 2016 7:18 pm
Forum: Vensim
Topic: DelayN with leakage?
Replies: 6
Views: 3743

Re: DelayN with leakage?

It seems like an array would be a reasonable solution, as long as your model isn't too big overall. For example, you could have a fixed-length array (say 100 levels) and vary the delay per level. That would allow you to vary the de facto delay order over any given horizon. Then, once calibrated, you...
by tomfid
Mon Feb 01, 2016 7:14 pm
Forum: Vensim
Topic: Binomial option pricing using Vensim
Replies: 9
Views: 5165

Re: Binomial option pricing using Vensim

It's very close to the Brownian motion example model I linked, and also to the Polya urn: http://models.metasd.com/polya-urn-with-increasing-returns/ I think this is what you're after: Binomial.mdl The tree isn't explicitly represented in the model (though you could probably do that with an array). ...
by tomfid
Mon Feb 01, 2016 7:00 pm
Forum: Ventity
Topic: Email problem
Replies: 1
Views: 2862

Re: Email problem

info@ventity.biz is the preferred address, but I've just enabled that one too.
by tomfid
Mon Feb 01, 2016 6:55 pm
Forum: Vensim
Topic: Auto regenerated hidden variables
Replies: 4
Views: 2531

Re: Auto regenerated hidden variables

You can promote a shadow variable to a regular variable with the "Model Variable" tool in Pro/DSS. That tool doesn't exist in PLE, because each variable has a regular instance that can't be converted to a shadow. However, it may be that there's some way to delete the primary instance in PL...
by tomfid
Fri Jan 29, 2016 3:40 am
Forum: Vensim
Topic: Data loss in SFD: how to trace?
Replies: 11
Views: 6960

Re: Data loss in SFD: how to trace?

I can open it and run it. It looks like templat.pdf but not diagram.pdf (presumably that is something else?). However, the structure is nonstandard. If I drag the shadow variables that appear below the stock elsewhere, I can see that they're connected with information arrows, rather than rates. Also...
by tomfid
Fri Jan 29, 2016 3:30 am
Forum: Vensim
Topic: Binomial option pricing using Vensim
Replies: 9
Views: 5165

Re: Binomial option pricing using Vensim

I can't remember if Binomial is in here, but this contains some stochastic processes:
http://models.metasd.com/stochastic-processes/

It can definitely be done. Also see
https://www.vensim.com/documentation/in ... zation.htm
which may be of use.
by tomfid
Thu Jan 28, 2016 2:35 pm
Forum: Vensim
Topic: DelayN with leakage?
Replies: 6
Views: 3743

Re: DelayN with leakage?

Sorry - haste makes for dumb answers. I can't see a way to do it without using arrays. What's the time horizon and mean time to failure? What makes the order so high? I wouldn't expect equipment to fail that way. Or is it a mix of failures and rules, such that things are replaced when they fail (low...
by tomfid
Wed Jan 27, 2016 12:44 am
Forum: Vensim
Topic: Data loss in SFD: how to trace?
Replies: 11
Views: 6960

Re: Data loss in SFD: how to trace?

Can you post the model and describe what disappeared?

This is not normal or common.
by tomfid
Tue Jan 26, 2016 7:31 pm
Forum: Vensim
Topic: DelayN with leakage?
Replies: 6
Views: 3743

Re: DelayN with leakage?

Would DELAY CONVEYOR work? That has leakage. https://www.vensim.com/documentation/in ... nveyor.htm
by tomfid
Mon Jan 25, 2016 8:18 pm
Forum: Vensim
Topic: Workforce modelling
Replies: 8
Views: 3934

Re: Workforce modelling

We're not just being pedantic here, by the way - getting the units right is a big aid to the reader. They make it easier to interpret variables. In my experience, fixing all the units errors in a model will identify at least a third of the bugs.
by tomfid
Mon Jan 25, 2016 8:09 pm
Forum: Vensim
Topic: modeling cyclical demand pattern into a constant variable
Replies: 6
Views: 3354

Re: modeling cyclical demand pattern into a constant variabl

You don't necessarily need to repeat the data four times in your lookup. You could do something like the following: demand = demand lookup( month index ) ~ widgets/month month index = MODULO( time, twelve months ) ~ dmnl twelve months == 12 ~ months The month index will then be a repeating index wit...
by tomfid
Wed Jan 20, 2016 8:28 pm
Forum: Vensim
Topic: How to force a value in a level variable?
Replies: 6
Views: 6089

Re: How to force a value in a level variable?

This is dimensionally inconsistent, because Level has units of stuff, and Rate has units of stuff/time.

The unit error is a hint that you are implicitly assuming TIME STEP = 1, which is not a good idea in general.
by tomfid
Mon Dec 14, 2015 2:39 pm
Forum: Vensim
Topic: How to force a value in a level variable?
Replies: 6
Views: 6089

Re: How to force a value in a level variable?

I tend to use something like the following: Indicated outflow = ... (something that could be too big) Actual outflow = MIN( Indicated outflow, Max outflow ) Max outflow = stock/min time to empty Min time to empty = ... (TIME STEP or greater) If there are multiple outflows, you can do something like:...
by tomfid
Sun Dec 13, 2015 4:21 am
Forum: Vensim
Topic: PLE can't import data from xls?
Replies: 4
Views: 2956

Re: PLE can't import data from xls?

This is a job for Pro or DSS.
by tomfid
Mon Dec 07, 2015 4:41 pm
Forum: Vensim
Topic: How to use "GET XLS LOOKUPS" and "LOOKUP EXTRAPOLATE" togeth
Replies: 6
Views: 3070

Re: How to use "GET XLS LOOKUPS" and "LOOKUP EXTRAPOLATE" to

Messages about an input exceeding the range of a lookup are just warnings, so that's probably not the problem. The origin of the floating point error is most likely something in the other dynamics of your model. One possible test would be to make the lookups flat (i.e. same output value for all inpu...
by tomfid
Sun Dec 06, 2015 5:48 am
Forum: Vensim
Topic: Combining variables with subscripts into a new variable
Replies: 3
Views: 2811

Re: Combining variables with subscripts into a new variable

If you map (sub1-sub5) to (a1-a5), (a6-a10) and (a11-a15), you should be able to do it in three equations. I'll have to scratch my head a bit to work out the details.
by tomfid
Mon Nov 30, 2015 3:34 pm
Forum: Vensim
Topic: building control panel (need help)
Replies: 10
Views: 4575

Re: building control panel (need help)

You could do something like: Data 1 = GET XLS ... Data 2 = GET XLS ... etc. Scenario = IF THEN ELSE( switch = 1, data 1, IF THEN ELSE( switch = 2, data 2, ... Make "switch" a constant with range 1 to 4 and interval 1, so you can easily select the source in synthesim. This can be done more ...
by tomfid
Wed Nov 25, 2015 4:21 pm
Forum: Ventity
Topic: cohort modeling examples
Replies: 21
Views: 15497

Re: cohort modeling examples

We haven't implemented discrete delays and the like yet, mainly because there hasn't been a request. My experience with conveyors with leakage and similar builtin functions is that I can never use them, because there's always some minor violation of the assumptions of the structure. So, I can think ...
by tomfid
Mon Nov 23, 2015 3:30 am
Forum: Vensim
Topic: Sensitivity Analysis
Replies: 1
Views: 1524

Re: Sensitivity Analysis

That's a PLE Plus (or higher) feature.

It wouldn't take too long to run a set of sims in synthesim, if you don't need a large sample.
by tomfid
Sat Nov 21, 2015 1:52 am
Forum: Vensim
Topic: Run a model but simultaneous equations involving
Replies: 7
Views: 5494

Re: Run a model but simultaneous equations involving

You have the Type for your stocks set to Auxiliary.

If, for example, you change the type of Population to Level, and enter an initial value, that eliminates the simultaneity. I think the other errors are similar.
by tomfid
Thu Nov 19, 2015 1:43 am
Forum: Vensim
Topic: Repeat time period with FINAL TIME as INITIAL CONDITION
Replies: 1
Views: 1455

Re: Repeat time period with FINAL TIME as INITIAL CONDITION

You can use the Based On simulation setting to reset the state variables - see https://www.vensim.com/documentation/23320.htm. This is SIMULATE>BASED in a command script. Not sure about iterating n times - you might do that with a command script, or using a programming language with the .dll.
by tomfid
Wed Nov 18, 2015 1:33 am
Forum: Vensim
Topic: Sensitivity Graph is not displayed
Replies: 1
Views: 1554

Re: Sensitivity Graph is not displayed

This may be due to screen resolution that's not sufficient to show everything. You can modify your toolset with Tools>Analysis Toolset>Modify, or shrink the icons with Tools>Options>Toolbars.
by tomfid
Mon Nov 16, 2015 6:49 pm
Forum: Vensim
Topic: How to model the different components of a mixture
Replies: 6
Views: 3685

Re: How to model the different components of a mixture

What exactly are you doing when this happens? Can you post a screenshot?

I have no trouble adding dimensions to your example.
subscripts.JPG
subscripts.JPG (66.91 KiB) Viewed 3542 times