Search found 2811 matches

by tomfid
Sun Sep 22, 2019 4:25 pm
Forum: Vensim
Topic: Converting flow into lookup
Replies: 1
Views: 129

Re: Converting flow into lookup

I can't view the model remotely, but you probably just need to change the type of the variable to "lookup".

See:
https://vensim.com/lookups-in-vensim/
http://vensim.com/documentation/usr08.htm
by tomfid
Sun Sep 22, 2019 4:20 pm
Forum: Vensim
Topic: Time Setting
Replies: 3
Views: 173

Re: Time Setting

Chapter 18 of the User Guide is a good example of a model calibrated against data:
http://vensim.com/documentation/usr18.htm
by tomfid
Sat Sep 21, 2019 3:02 pm
Forum: Vensim
Topic: Time Setting
Replies: 3
Views: 173

Re: Time Setting

Same file for sure. What you want is a dynamic structure that replicates the data over the historical period, then runs into the future for projections.
by tomfid
Fri Sep 20, 2019 3:33 pm
Forum: Vensim
Topic: Uploading Data onto Vensim PLE
Replies: 27
Views: 5680

Re: Uploading Data onto Vensim PLE

I'm on the road and can't modify the model, plus I don't have the data. But the structure you already have for "fit degression rate" is exactly what you need. "FIT degression rate DATA" is the lookup and "FIT degression rate" is the value looked up from the data, by time.
by tomfid
Fri Sep 20, 2019 3:28 pm
Forum: Vensim
Topic: Help - please
Replies: 2
Views: 148

Re: Help - please

Is this a data variable? If so, the line won't extend past the end of the data.
by tomfid
Tue Sep 17, 2019 9:18 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 35
Views: 1754

Re: sensitivity analysis (vensim)

I think the "wrong type" error only occurs if a variable is not a constant (the "not found" is misleading). Most likely causes are setting the constant subtype to unchangeable (with ==), setting the type to initial(), or simply specifying a nonnumeric expression for the variable, like x*y or 3/4.
by tomfid
Tue Sep 17, 2019 6:01 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 35
Views: 1754

Re: sensitivity analysis (vensim)

I think the second error is a consequence of the first. It's not finding Yearly Depreciation Factor, and therefore not adding it as an input. Are there other parameters in the vsc?

Does Yearly Depreciation Factor have an array dimension? It's not set to "Initial" type by accident?
by tomfid
Tue Sep 17, 2019 5:03 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 35
Views: 1754

Re: sensitivity analysis (vensim)

Sounds like your control file (.vsc) specifies a variable that doesn't exist or isn't constant.
by tomfid
Sun Sep 15, 2019 5:12 pm
Forum: Vensim
Topic: Uploading Data onto Vensim PLE
Replies: 27
Views: 5680

Re: Uploading Data onto Vensim PLE

It would be exactly the same structure as you have for FIT Degression Rate.
by tomfid
Fri Sep 13, 2019 5:56 pm
Forum: Vensim
Topic: Uploading Data onto Vensim PLE
Replies: 27
Views: 5680

Re: Uploading Data onto Vensim PLE

Normally you would specify the data file in the Data Sources... field, on the Advanced tab of the simulation control dialog (Model>Simulate menu).

However, PLE doesn't do data variables, so you'd have to use another lookup.
by tomfid
Tue Sep 10, 2019 12:32 am
Forum: Vensim
Topic: Reference for Vensim's automatic calibration
Replies: 4
Views: 270

Re: Reference for Vensim's automatic calibration

You could cite: Powell, M. J. D. (1964). "An efficient method for finding the minimum of a function of several variables without calculating derivatives". Computer Journal. 7 (2): 155–162. doi:10.1093/comjnl/7.2.155. Press, WH; Teukolsky, SA; Vetterling, WT; Flannery, BP (2007). "Section 10.7. Direc...
by tomfid
Mon Sep 09, 2019 2:48 pm
Forum: Vensim
Topic: Random Number generation
Replies: 1
Views: 140

Re: Random Number generation

The scale parameter determines the mean (assuming shift=0 and there is no truncation), and therefore is the inverse of the lambda parameter typically described for the distribution. The standard deviation equals the mean (variance = mean^2). So, you could use shift=0 and scale=mean of your data. See...
by tomfid
Tue Sep 03, 2019 2:16 pm
Forum: Vensim
Topic: Vensim 8 External functions documents & help
Replies: 8
Views: 473

Re: Vensim 8 External functions documents & help

I think it's a terminology gap. If Microsoft uses "workload" to mean which language package is active in Viz Studio, then yes, C++ is what you want.
by tomfid
Tue Sep 03, 2019 2:15 pm
Forum: Vensim
Topic: connecting vensim and online data
Replies: 2
Views: 194

Re: connecting vensim and online data

Depends what you mean by "connect." There are multiple ways to use data in Vensim, and many online climate sources. If you want to scrape data off the web, you'll probably have to write some custom code, but you'd have to tell us more about your use case for advice about how to get it into Vensim. I...
by tomfid
Tue Sep 03, 2019 2:13 pm
Forum: Vensim
Topic: Reference for Vensim's automatic calibration
Replies: 4
Views: 270

Re: Reference for Vensim's automatic calibration

Which algorithm are you using? Powell or MCMC?
by tomfid
Tue Sep 03, 2019 2:12 pm
Forum: Vensim
Topic: Graph export at high resolution (>=300 dpi)
Replies: 3
Views: 219

Re: Graph export at high resolution (>=300 dpi)

Pasting into Paint may be your problem. That throws away the vector graphic and gives you some kind of bitmap. Paste into Word, Powerpoint, or a vector drawing program.
by tomfid
Fri Aug 30, 2019 9:49 pm
Forum: Ventity
Topic: Initializing Entities from a stack?
Replies: 6
Views: 433

Re: Initializing Entities from a stack?

Here are a couple variations. In the "PL1" version, I made the process list approach a little fancier.

In the "2" version, I switched to a linked list.
projectStack.zip
(31.95 KiB) Downloaded 28 times
by tomfid
Fri Aug 30, 2019 10:22 am
Forum: Ventity
Topic: Initializing Entities from a stack?
Replies: 6
Views: 433

Re: Initializing Entities from a stack?

I'll take a look. I'm not sure about "more elegant" but you could avoid the process list by making the stack into a linked list by adding a "next in stack" attribute to each stack item. On the other hand, the process list is nice because you could change the priority for selecting the next item dyna...
by tomfid
Fri Aug 30, 2019 10:05 am
Forum: Vensim
Topic: Structure and vensim equations for the macro "DELAY FIXED"
Replies: 2
Views: 193

Re: Structure and vensim equations for the macro "DELAY FIXED"

It's an infinite order delay, which means that effectively it's an aging chain where the number of stocks is equal to delay_duration/TIME_STEP, and each stock has time constant = TIME_STEP.
by tomfid
Thu Aug 29, 2019 1:41 am
Forum: Vensim
Topic: Use of time zone in Vensim
Replies: 4
Views: 210

Re: Use of time zone in Vensim

Seems like more of a discrete event simulation problem.

You could assign each team member an integer time zone number, and search for viable times that are within a certain window overlap from the zone number, modulo 24.

It's hard to say more without knowing more about the problem statement.
by tomfid
Wed Aug 28, 2019 5:53 pm
Forum: Ventity
Topic: summing over data entity types
Replies: 1
Views: 219

Re: summing over data entity types

Possibly - we'll check it out.

As a workaround, you could move the numbers over to a regular entity and aggregate there.
by tomfid
Wed Aug 28, 2019 3:15 am
Forum: Vensim
Topic: Use of time zone in Vensim
Replies: 4
Views: 210

Re: Use of time zone in Vensim

What do you want to do with the time zone? How about using an integer from 1 to 24?
by tomfid
Mon Aug 26, 2019 2:42 pm
Forum: Vensim
Topic: data science
Replies: 2
Views: 177

Re: data science

There are many that implement large portions of this. Here's one example:
https://scholar.harvard.edu/jalali/publ ... e-petition
There's a version in the SD conference proceedings that includes the model.
by tomfid
Mon Aug 26, 2019 2:22 pm
Forum: Ventity
Topic: changing the "Map Layer"
Replies: 3
Views: 293

Re: changing the "Map Layer"

You can use the tooltip field. Not sure what the status is, but here's the latest from the dev team: The current tooltip implementation goes as follows : 1) You can put any text you want 2) some html formatting applies, like <br> for new line and <b></b> for bold 3) variables are introduced using cu...
by tomfid
Mon Aug 26, 2019 2:18 pm
Forum: Vensim
Topic: Using more than two Subscripts
Replies: 6
Views: 267

Re: Using more than two Subscripts

If most of your values are 0, you can put 0 in the equation,
const[x,y,z] = 0

Then use a .cin file to override the few nonzero values:
const[b,y2,z1] = 3.141