Search found 2091 matches

by tomfid
Wed Feb 21, 2018 6:33 pm
Forum: Vensim
Topic: Export variables
Replies: 1
Views: 14

Re: Export variables

Yes - you can specify a savelist in the export dialog, or at runtime (the first is usually preferred).

Another option is to simply use the table tool and copy-paste.

http://vensim.com/documentation/ref_savelist.htm
http://vensim.com/documentation/23500.htm
by tomfid
Tue Feb 20, 2018 10:51 pm
Forum: Vensim
Topic: Optimization in Vensim
Replies: 3
Views: 28

Re: Optimization in Vensim

Whether a vdf is needed or not depends on the data import method.

If you're using GET XLS DATA for everything, no vdf is required.

Otherwise, if you're importing data from text or spreadsheets, you do need the vdf - but you must already have it if your model is working now.
by tomfid
Tue Feb 20, 2018 8:51 pm
Forum: Vensim
Topic: Optimization in Vensim
Replies: 3
Views: 28

Re: Optimization in Vensim

I'm not sure you need to change your method - there are really 2 approaches that work. Option 1 is what you've done, which is to have a model variable (imports) and a corresponding data variable (data imports). Then your payoff has to explicitly specify both, which will look like model variable|data...
by tomfid
Tue Feb 20, 2018 6:29 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 149

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Good comments, JJ.

I still have a post edit button - possibly it's a momentary glitch or browser issue?
by tomfid
Tue Feb 20, 2018 4:46 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 149

Re: Optimization - VECTOR LOOKUP and other approaches ?)

There are several ways to make a hybrid that is target-responsive, but more accurately cost minimizing. Generally, you need more flexibility in the functional form: - more inputs - nonlinear transformations of the inputs - advance information about the inputs (for example, policies are typically ann...
by tomfid
Tue Feb 20, 2018 4:41 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 149

Re: Optimization - VECTOR LOOKUP and other approaches ?)

I think the appropriate choice depends on the context. - If there's a single fleet manager making decisions with a lot of information, the VECTOR LOOKUP approach is reasonable, especially if you modify it to make it responsive to uncertainty or variation in the target. - If the decision is distribut...
by tomfid
Thu Feb 15, 2018 3:41 pm
Forum: Vensim
Topic: Problem using NORMAL RANDOM
Replies: 5
Views: 71

Re: Problem using NORMAL RANDOM

Correct - the logic matches the wiki page, which is the standard way of describing a truncated Normal in areas I'm familiar with.

You can use the NORMAL CDF function if you need to determine the mean realized from a particular combination of parameters.
by tomfid
Thu Feb 15, 2018 3:36 pm
Forum: Vensim
Topic: Problem using NORMAL RANDOM
Replies: 5
Views: 71

Re: Problem using NORMAL RANDOM

Taking x = MIN(1,MAX(0,RANDOM NORMAL(-1000,1000,0,1,0))) gives different results from y = RANDOM NORMAL(0,1,0,1,0) When you wrap the normal in MIN MAX, an out-of-range value gets truncated to the MIN or MAX endpoint. This causes a peak in the histogram at the ends. When the RANDOM NORMAL function ex...
by tomfid
Thu Feb 15, 2018 3:26 pm
Forum: Vensim
Topic: Importing Data from Excel (24 hours in a year)
Replies: 5
Views: 49

Re: Importing Data from Excel (24 hours in a year)

You can't directly import a 2-dimensional table like your solar radiation table, except as an array of constants. Some options: 1. Import the table as an array with GET XLS CONSTANTS, and then use rows of it with VECTOR LOOKUP 2. Using copy-paste, create a separate lookup table each for Jan, Feb, Ma...
by tomfid
Wed Feb 14, 2018 11:08 pm
Forum: Vensim
Topic: SENS2TAB supports appending? +
Replies: 12
Views: 67

Re: SENS2TAB supports appending? +

Right. I've tried the same experiment - XP is missing some needed resources (and Microsoft support for it ended 4 years ago).
by tomfid
Wed Feb 14, 2018 9:23 pm
Forum: Vensim
Topic: SENS2TAB supports appending? +
Replies: 12
Views: 67

Re: SENS2TAB supports appending? +

What OS is on your old VM?
by tomfid
Wed Feb 14, 2018 3:47 pm
Forum: Vensim
Topic: Converting INITIAL to AUXILIARY globally
Replies: 2
Views: 31

Re: Converting INITIAL to AUXILIARY globally

BTW I wouldn't guarantee that any of this will actually produce desirable results. Some of those INITIALs may be there for good reasons. If the problematic chains are something like, constant x -> INITIAL( f(x) ) -> dynamics and you want GAME(x) -> f(x) -> dynamics, it's not clear that the dynamics ...
by tomfid
Wed Feb 14, 2018 3:40 pm
Forum: Vensim
Topic: Converting INITIAL to AUXILIARY globally
Replies: 2
Views: 31

Re: Converting INITIAL to AUXILIARY globally

If you're working in DSS, you could do the following: 1. Create a macro called something like MIGHT_BE_INITIAL, which returns INITIAL(x), but could be instantly changed to just return (x). 2. Search and replace all instances of INITIAL( to MIGHT_BE_INITIAL( If you're not using DSS, you could search ...
by tomfid
Tue Feb 13, 2018 5:51 pm
Forum: Vensim
Topic: Optimization - VECTOR LOOKUP and other approaches ?)
Replies: 13
Views: 149

Re: Optimization - VECTOR LOOKUP and other approaches ?)

Here's a closed-loop alternative. Fuel economy goal seeking_test_approach 3.mdl I've made the choice of car a function of price and fuel economy. The weight to fuel economy varies with the gap between the standard and actual stock performance. This introduces a few new parameters (orange). It's not ...
by tomfid
Tue Feb 13, 2018 5:43 pm
Forum: Vensim
Topic: SENS2TAB supports appending? +
Replies: 12
Views: 67

Re: SENS2TAB supports appending? +

What does your help file say for SENS2TAB? It's likely that the feature was added when we added SENS2FILE, in 6.4.
by tomfid
Tue Feb 13, 2018 4:07 pm
Forum: Vensim
Topic: SENS2TAB supports appending? +
Replies: 12
Views: 67

Re: SENS2TAB supports appending? +

I think so, with the same + keyword.
by tomfid
Tue Feb 13, 2018 3:05 pm
Forum: Vensim
Topic: multi dimensioal array
Replies: 19
Views: 161

Re: multi dimensioal array

... or, if you want SBP to be a static function of age, so that it doesn't move with the cohorts, the *0 might be the right thing to do. You could also eliminate the SBP flow dynamics easily, and treat it like an array or lookup.
by tomfid
Tue Feb 13, 2018 2:59 pm
Forum: Vensim
Topic: multi dimensioal array
Replies: 19
Views: 161

Re: multi dimensioal array

So the problem is that it misbehaves when you remove the *0 from SBP aging?

One suggestion: define units for the whole model. That might reveal an issue that's easy to overlook.
by tomfid
Tue Feb 13, 2018 5:17 am
Forum: Vensim
Topic: vensim function
Replies: 5
Views: 49

Re: vensim function

x=TIME BASE(0,1)

is the same as

x = Time

when INITIAL TIME=0 and TIME STEP=1.
by tomfid
Mon Feb 12, 2018 2:41 pm
Forum: Vensim
Topic: vensim function
Replies: 5
Views: 49

Re: vensim function

Or just use INTEGER(Time).

However, you should avoid creating something that's tied to a particular time step. http://metasd.com/2017/11/discrete-time-stinks/
by tomfid
Mon Feb 12, 2018 2:39 pm
Forum: Vensim
Topic: vensim function
Replies: 5
Views: 49

Re: vensim function

Create a stock, with inflow 1/TIME STEP?
by tomfid
Fri Feb 09, 2018 4:18 pm
Forum: Vensim
Topic: Odd panel behaviour in Vensim
Replies: 1
Views: 31

Re: Odd panel behaviour in Vensim

Strange. You might try reinstalling with the option checked to overwrite the settings in vensim.ini (or simply find & delete/rename your vensim.ini, so it gets rebuilt).
by tomfid
Fri Feb 09, 2018 4:17 pm
Forum: Vensim
Topic: Data import
Replies: 8
Views: 53

Re: Data import

In the data field on the Advanced tab, you should be specifying a .vdf file that you previously imported from Excel (or from another model, .tab delimited, etc.). Listing a spreadsheet there won't work. Warnings about "Simulation starts before first time for exogenous variable" can usually...
by tomfid
Thu Feb 08, 2018 8:46 pm
Forum: Vensim
Topic: Data import
Replies: 8
Views: 53

Re: Data import

Have you specified your data.vdf in the data field, on the Advanced tab of the Simulation Control dialog?

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