Search found 2234 matches

by tomfid
Fri May 25, 2018 12:20 pm
Forum: Vensim
Topic: "show" and "hide" commands in Venapp
Replies: 3
Views: 10

Re: "show" and "hide" commands in Venapp

You could have 4 versions of the screen, and jump to the appropriate one based on the distribution selected?
by tomfid
Thu May 24, 2018 12:10 pm
Forum: Vensim
Topic: Return degraded state to a certain value
Replies: 11
Views: 81

Re: Return degraded state to a certain value

Your case should just be the negative of the solution above:

stock = INTEG( - flow + reset, init val )
reset = (desired stock - stock)/TIME STEP + flow
by tomfid
Thu May 24, 2018 12:08 pm
Forum: Vensim
Topic: Opening "Sensitivity Simulation Setup" window in Venapp
Replies: 4
Views: 29

Re: Opening "Sensitivity Simulation Setup" window in Venapp

The parameters of the distribution in the sensitivity control can be variables, and the user can set the values of those like other constants. If you want the user to choose the distribution as well, you'd have to build that into the model. Then the user could set a flag to choose the distribution, ...
by tomfid
Wed May 23, 2018 6:30 pm
Forum: Vensim
Topic: overriding a subscripted variable in synthesim
Replies: 1
Views: 10

Re: overriding a subscripted variable in synthesim

In the Subscript Control, make the element you want to override the first (or only) active selection, then do your override.
by tomfid
Wed May 23, 2018 12:18 am
Forum: Ventity
Topic: setting an attribute in a create action
Replies: 2
Views: 29

Re: setting an attribute in a create action

Here's a workaround, using a Process List action. It's a little more complex to set up, but generally it's a lot better because (a) there's no possibility of errors (a Buyer getting a reference to a Vendor that doesn't exist) (b) you can change the size of the Vendor list just by changing the initia...
by tomfid
Tue May 22, 2018 10:42 pm
Forum: Ventity
Topic: Ventity 1.3 Release
Replies: 0
Views: 6

Ventity 1.3 Release

Ventity release 1.3 has arrived! Much of what’s new is under the hood, including big performance improvements and infrastructure to support deployment as a web service, with Forio support coming soon. There’s also a new architecture for lookup tables, with functions for extrapolation and finding the...
by tomfid
Tue May 22, 2018 10:17 pm
Forum: Ventity
Topic: setting an attribute in a create action
Replies: 2
Views: 29

Re: setting an attribute in a create action

I think this may be a glitch in the if-then-else code for attributes. I'm investigating & will report back ASAP.
by tomfid
Tue May 22, 2018 5:29 pm
Forum: Vensim
Topic: Return degraded state to a certain value
Replies: 11
Views: 81

Re: Return degraded state to a certain value

Great!
by tomfid
Tue May 22, 2018 12:35 pm
Forum: Vensim
Topic: Return degraded state to a certain value
Replies: 11
Views: 81

Re: Return degraded state to a certain value

"reset" is an additional variable.
by tomfid
Tue May 22, 2018 3:35 am
Forum: Vensim
Topic: problem in initializing my model in equilibrium “Simultaneous initial value equation involving…”
Replies: 4
Views: 44

Re: problem in initializing my model in equilibrium “Simultaneous initial value equation involving…”

Notice also that MIN( Local inventory, Shipment requirement) is dimensionally inconsistent - MIN( widgets, widgets/time ) is not valid. I'd encourage you to define units for the whole model before you get much further.
by tomfid
Tue May 22, 2018 3:33 am
Forum: Vensim
Topic: problem in initializing my model in equilibrium “Simultaneous initial value equation involving…”
Replies: 4
Views: 44

Re: problem in initializing my model in equilibrium “Simultaneous initial value equation involving…”

Generally the thing to do in nonlinear cases like this is to assume that the inventory constraint is nonbinding, i.e. shipment = shipment requirement.
by tomfid
Mon May 21, 2018 2:40 pm
Forum: Vensim
Topic: Question about TIME STEP and delays
Replies: 4
Views: 32

Re: Question about TIME STEP and delays

In a literal sense, the software does operate in discrete time, because a digital computer can't really do anything continuously. But it's desirable for the model to be independent of any particular discrete time step as much as possible. This is particularly true if you're using RK integration, whe...
by tomfid
Mon May 21, 2018 2:31 pm
Forum: Vensim
Topic: VECTOR ELM MAP - how to avoid error messages and set NA to 0?
Replies: 5
Views: 31

Re: VECTOR ELM MAP - how to avoid error messages and set NA to 0?

You could use VECTOR SELECT, which has an argument for missing values.
by tomfid
Sun May 20, 2018 4:18 pm
Forum: Vensim
Topic: problem in initializing my model in equilibrium “Simultaneous initial value equation involving…”
Replies: 4
Views: 44

Re: problem in initializing my model in equilibrium “Simultaneous initial value equation involving…”

The circularity is listed in the error report: ERROR: Simultaneous initial value equations involving: InTansit. : Inventory position. : Order decision. : Demand2. : Shipment requirement2. : Shipment2. : InTansit. In general, a stock initial value expression can't refer to itself, however indirectly....
by tomfid
Thu May 17, 2018 5:21 pm
Forum: Vensim
Topic: Model CDF without a closed-form solution
Replies: 8
Views: 70

Re: Model CDF without a closed-form solution

Correct, but you can't use VECTOR LOOKUP with DELAY PROFILE.
by tomfid
Thu May 17, 2018 5:20 pm
Forum: Vensim
Topic: Question about TIME STEP and delays
Replies: 4
Views: 32

Re: Question about TIME STEP and delays

It's generally better to avoid discrete delays like DELAY FIXED and use continuous stocks & flows instead. See:
http://metasd.com/2017/11/discrete-time-stinks/

There are also several examples of continuous energy-economic models here:
http://metasd.com/model-library/
by tomfid
Thu May 17, 2018 2:00 pm
Forum: Vensim
Topic: Model CDF without a closed-form solution
Replies: 8
Views: 70

Re: Model CDF without a closed-form solution

It's based on the macro from MetaSD that Tony linked - same inputs.

I'll add it to the help.
by tomfid
Thu May 17, 2018 12:19 pm
Forum: Vensim
Topic: Model CDF without a closed-form solution
Replies: 8
Views: 70

Re: Model CDF without a closed-form solution

Note that the NORMAL CDF macro is now built-in to Vensim. The numerical approximation is quite precise; I think it would be rare to find a case where any error was meaningful relative to other uncertainties in the model.

For other distributions, you could write an external function.
by tomfid
Wed May 16, 2018 1:56 pm
Forum: Vensim
Topic: Return degraded state to a certain value
Replies: 11
Views: 81

Re: Return degraded state to a certain value

The generic approach is as follows. You have: stock = INTEG( flow, init val ) you can reset the stock with: stock = INTEG( flow + reset, init val ) reset = (desired stock - stock)/TIME STEP - flow In other words, the reset has to (a) adjust the stock toward the desired value (which might be init val...
by tomfid
Wed May 16, 2018 1:06 pm
Forum: Vensim
Topic: Global Carbon Cycle Example
Replies: 5
Views: 61

Re: Global Carbon Cycle Example

If you post your error, we might be able to help. Also, the models I posted should be error-free.
by tomfid
Wed May 16, 2018 1:06 pm
Forum: Vensim
Topic: Global Carbon Cycle Example
Replies: 5
Views: 61

Re: Global Carbon Cycle Example

This model has a lot of parameters embedded as numbers in equations. For example: *********************************************** Error in units for the following equation: CO2 absorption = 92 * ( Atmosphere / 750) CO2 absorption --> Gt/yr Atmosphere --> Gt Analysis of units error: Right hand and le...
by tomfid
Mon May 14, 2018 8:03 pm
Forum: Vensim
Topic: PLE+ equation editor font : can't change
Replies: 8
Views: 71

Re: PLE+ equation editor font : can't change

You can download again, or you can also just copy the installer over to the new machine.

What are your font scaling settings in the Display control panel?
by tomfid
Mon May 14, 2018 6:24 pm
Forum: Vensim
Topic: Global Carbon Cycle Example
Replies: 5
Views: 61

Re: Global Carbon Cycle Example

http://metasd.com/2014/07/free/
http://metasd.com/2010/06/dice/

Generally, atmospheric CO2 is measured in GtC (gigatons carbon), with the corresponding emissions and uptake flows in GtC/year. But you'll often find emissions in GtCO2 terms - a ton of CO2 is 44/12 tons of C.
by tomfid
Mon May 14, 2018 1:01 pm
Forum: Vensim
Topic: PLE+ equation editor font : can't change
Replies: 8
Views: 71

Re: PLE+ equation editor font : can't change

Courier 9 or Microsoft Sans 9, 10 generally work fine.

This may interact with the operating system's font scaling in the Display control panel.

How big is your screen (physical size, not resolution)?

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