Ventana Systems UK Forum

Vensim :: Re: overriding a subscripted variable in synthesim :: Reply by LAUJJL

2012-05-18T12:44:44+00:00

Hi Tom and Tony

Thank you both for the answers.

Regards.

JJ

Vensim :: external functions / user loops / which subscript :: Author etam

2012-05-18T16:29:02+00:00

I want to write an external function, that has a user loop, so it's quickly fills a vector with some values.
It works fine for all elements of a vector, but what if I do not want to use/fill all elements?

Code: Select all: MainRange: e1, e2, e3, e4 ~~| SubRange: e1, e3 ~~| B[MainRange]=MyExternalFunction(A[MainRange]) ~~| C[SubRange]=MyExternalFunction(A[SubRange]) ~~|

Is there a way to figure out inside the external function (c code) which subscript range is used currently in the equation (MainRange or SubRange)?

Thx

Vensim :: Re: external functions / user loops / which subscript :: Reply by tomfid

2012-05-18T17:02:43+00:00

Before we get into the details, what is this trying to accomplish it, and why is it impossible in Vensim alone? (There might be an easier way.)

Vensim :: Re: external functions / user loops / which subscript :: Reply by etam

2012-05-18T17:03:30+00:00

And do I think well that the values of a vector variable are in the same order as the main subscript range elements?
So VECTOR_ARG->vals[ i] goes to the ith element of the main range.

That means, if I knew what subscript (sub)range is used in that equation, I could get its elements and its main range and its elements via vensim_get_varattrib. Based on this info I can get the indices what to use in the vals array for the subrange case.

Can you see any problems in this logic? I couldn't find all info in the documentation that would ensure that but I guess it has to be the case, not?
Of course for this you have to know the subscript range used during the external function call.

Vensim :: Re: external functions / user loops / which subscript :: Reply by etam

2012-05-18T17:04:45+00:00

It's an optimizing task I have to put into the model (dispatching like thing).
The ALLOC functions are not good for me.

2002 :: Limitations of System dynamics? :: Reply by "Ray on EV1"

2020-10-14T19:31:33+00:00

The system dynamics methods are suitable in general. But changing paths in
the middle of a project might be more catastrophic than your current
situation.

You should re-think where you are: Your experienced in UML, your client is
not communicating well with your programmers. Communication difficulties in
UML have two typical sources - the facilitator doesnt know UML that well,
the participants dont really know the field they are expected to be
experienced in. SD has the advantage of not requiring either but you must
understand the methods. Since you are familiar with UML, you might consider
that your client isnt actually a domain expert in the material he is
supposed to provide. This is common for an executive on a tight budget not
wanting to allocate personnel to a project. You might also consider where
as you are familiar with UML and understand the process, you may not be well
versed at carrying (facilitating) others along.

So you are in the middle of a project and dont see the resources you need
to progress. Consider canceling the project and cutting short your clients
losses, or bring in a facilitator for one of the two methodologies.

Ray
From: "Ray on EV1"