Search found 2813 matches

by tomfid
Mon Dec 23, 2019 5:45 am
Forum: Vensim
Topic: Maximum value
Replies: 26
Views: 1479

Re: Maximum value

This seems to be working fine. T2 and T2max both reach their max values at time 2. What's the problem?
by tomfid
Fri Dec 20, 2019 4:40 pm
Forum: Vensim
Topic: Changing vdf data sources from Excel using dll
Replies: 4
Views: 120

Re: Changing vdf data sources from Excel using dll

Nope - a vdf output from one model can be read directly as input to another model. No conversion needed - you just need to have matching variable names.
by tomfid
Thu Dec 19, 2019 4:57 pm
Forum: Vensim
Topic: Changing vdf data sources from Excel using dll
Replies: 4
Views: 120

Re: Changing vdf data sources from Excel using dll

I would recommend importing the spreadsheet to a vdf and using ordinary data variables rather than the GET VDF functions. Then you can control the data source via SIMULATE>DATA| and ADDDATA.
by tomfid
Thu Dec 19, 2019 4:56 pm
Forum: Vensim
Topic: Bugs?
Replies: 1
Views: 65

Re: Bugs?

1 & 3 are known and will be fixed in the next release. We'll look into #2.
by tomfid
Tue Dec 17, 2019 5:24 pm
Forum: Vensim
Topic: Misterious Calculation not computed
Replies: 4
Views: 104

Re: Misterious Calculation not computed

A possible test would be to compute SUM(Alfa[Sub!]) in a separate variable.
by tomfid
Fri Dec 13, 2019 3:27 pm
Forum: Vensim
Topic: Getting the final value of a stock to another variable
Replies: 5
Views: 123

Re: Getting the final value of a stock to another variable

More importantly, using the value of a variable at FINAL TIME to set the value of another stock at INITIAL TIME is acausal, i.e. it implies effect preceding cause. You can't do that in Vensim by design, because no one really knows the future.
by tomfid
Thu Dec 12, 2019 2:48 am
Forum: Vensim
Topic: Does Vensim embed loop intervals?
Replies: 6
Views: 157

Re: Does Vensim embed loop intervals?

I think the thing to do is to discretize the LDC into a number of segments, represented by an array dimension. Then you can compute utilization of each plant type in each segment. Then the price is the highest-cost plant with nonzero utilization in the segment. (The allocation functions might make t...
by tomfid
Wed Dec 11, 2019 11:59 pm
Forum: Vensim
Topic: Does Vensim embed loop intervals?
Replies: 6
Views: 157

Re: Does Vensim embed loop intervals?

No problem - we can delete one. Is this the better copy?
by tomfid
Wed Dec 11, 2019 11:18 pm
Forum: Ventity
Topic: Time Series Data Runtime Warnings
Replies: 3
Views: 180

Re: Time Series Data Runtime Warnings

Great! At some point, we'll have data entity singletons, so you don't have to bother with creating a key value for something that has only one instance anyway, as here.
by tomfid
Wed Dec 11, 2019 7:21 pm
Forum: Ventity
Topic: Time Series Data Runtime Warnings
Replies: 3
Views: 180

Re: Time Series Data Runtime Warnings

Hi - You're really close. The data is actually OK. You can verify this in the results: vresults.png The issue is the references in the Growth entitytype. You have 3: Grass6 GrassDataID GrassGrow (These can be found in the References tab of the Growth inspector.) GrassDataID is the reference correspo...
by tomfid
Mon Dec 09, 2019 8:04 pm
Forum: Ventity
Topic: Integration method
Replies: 3
Views: 111

Re: Integration method

OK, thanks for the feedback.

The things we'd probably consider, in descending order of priority, would be:
- RK4auto
- RK2/4 fixed
- An implicit method
An Eigenvector method would be cool, but unfortunately not compatible with action scheduling.
by tomfid
Mon Dec 09, 2019 6:32 pm
Forum: Ventity
Topic: Integration method
Replies: 3
Views: 111

Re: Integration method

At some point, yes, but we haven't had any signals from the user base that it's a priority. What are you looking for?
by tomfid
Sat Dec 07, 2019 12:32 am
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 31
Views: 1978

Re: Integrating time step of optimization problem

Ah - that explains the difference. Seems like a weird way to run a market, but if those are the rules, those are the rules. Here's an idea: Suppose generators bid at cost + markup Make the markup a stock, which bidders adjust according to some pressures - e.g., maintaining a desired utilization (sub...
by tomfid
Fri Dec 06, 2019 8:53 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 31
Views: 1978

Re: Integrating time step of optimization problem

Is there a reason to to have bidders bid at their own marginal cost, per theory?
by tomfid
Fri Dec 06, 2019 4:58 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 31
Views: 1978

Re: Integrating time step of optimization problem

Not sure where the original thread is, but I think the problem may be that inclusion of expected price in bid formation is not rational or competitive, hence the apparent violation of theory.
by tomfid
Fri Dec 06, 2019 3:57 pm
Forum: Vensim
Topic: Random arrival rate
Replies: 1
Views: 75

Re: Random arrival rate

Typically you'd use Poisson and Binomial distributions for that. Example: https://metasd.com/2010/04/rental-car-s ... -dynamics/
by tomfid
Thu Dec 05, 2019 2:36 pm
Forum: Vensim
Topic: Power function - problem with units
Replies: 7
Views: 952

Re: Power function - problem with units

You're correct - the aggregate SD approach with continuous payments and infinite horizon never fully repays the loan. There are alternatives. One is to maintain more states for the loan. For example, the principal plus the term remaining. Then you can work out the remaining level payment at any poin...
by tomfid
Sat Nov 30, 2019 6:28 pm
Forum: Ventity
Topic: Using actions to change stock values
Replies: 1
Views: 124

Re: Using actions to change stock values

1. Drag a copy of the target stock onto the action diagram (using the parent or invoker reference) 2. Add an inflow to the stock. 3. Set the inflow equation for the stock to = newValue-stock Note that the units on this flow are the same as the stock (unlike a normal dynamic equation where flow = sto...
by tomfid
Mon Nov 25, 2019 3:45 pm
Forum: Vensim
Topic: A question about Allocate available function
Replies: 3
Views: 146

Re: A question about Allocate available function

The immediate problem here is that you can only use a comma-separated list for constant values (i.e. numbers).
https://www.vensim.com/documentation/21265.htm
by tomfid
Sat Nov 23, 2019 12:47 pm
Forum: Vensim
Topic: Combining Lookup Variables
Replies: 5
Views: 172

Re: Combining Lookup Variables

If the point is to combine a bunch of conflicting schedule elements in a static way, which is what lookups would do, you could pre-combine the lookup tables in a spreadsheet and plug the result into the model. If it's something else, I'd have to understand more about the dynamics to be represented i...
by tomfid
Fri Nov 22, 2019 2:15 am
Forum: Vensim
Topic: Combining Lookup Variables
Replies: 5
Views: 172

Re: Combining Lookup Variables

How about something like:

working = work_lookup(time)
sleeping = sleep_lookup(time)
busy = IF THEN ELSE( working :OR: sleeping, 0, 1 )

?
by tomfid
Wed Nov 20, 2019 1:03 pm
Forum: Ventity
Topic: "The configuration is read only" error
Replies: 13
Views: 551

Re: "The configuration is read only" error

If the .NET framework update doesn't work for you, email us at info at ventity.biz - we now have a build that removes the dependency. This will be in an official release soon.
by tomfid
Tue Nov 19, 2019 4:12 pm
Forum: Ventity
Topic: "The configuration is read only" error
Replies: 13
Views: 551

Re: "The configuration is read only" error

Installing the latest .NET framework solved the problem in at least 1 case:
Download: https://dotnet.microsoft.com/download/dotnet-framework
Check: https://docs.microsoft.com/en-us/dotnet ... -installed
by tomfid
Tue Nov 19, 2019 4:08 pm
Forum: Ventity
Topic: connection with other softwares
Replies: 1
Views: 82

Re: connection with other softwares

We definitely have this on our road map. However, these capabilities are currently not very high on the priority list, due to perceived lack of demand. We'd be interested in hearing other votes for such things.
by tomfid
Wed Nov 13, 2019 10:06 pm
Forum: Vensim
Topic: Vensim flicks and flips off completely sometimes
Replies: 13
Views: 250

Re: Vensim flicks and flips off completely sometimes

Does this happen when you are editing the diagram - adding arrows, moving variables, etc. - or when you're in the equation editor?