call external function

GAMS
1

Hi,

I want to define a constraint like this:

x1 + callfun(x2) =E= 1;

callfun(x2) is a function exists in MATLAB directory.

Is it possible to call it from GAMS?

if no, MATLAB code can be converted to C# (dll) and then the dll can be used as an external function?

Thank you

2

GAMS can work with a DLL (but this needs to provide a special function API). See external equations (https://www.gams.com/24.9/docs/UG_ExternalEquations.html) or extrinsic functions (https://www.gams.com/24.9/docs/UG_ExtrinsicFunctions.html). Key is that you have to provide the derivative for this function to use it in a solver.

Hope this helps,
-Michael

3

Michael,

The function - callfun(x2) - get x2 and then return an int value. It has no derivation. I tried to make dll in c# like this

Public static int callfun(int x_in)
{
x_in = x_in + 1
Return x_in
}

When I imported it through $Funlibin, I encountered a problem regarding loading error.

In guidelines written different programming languages are compatible, becoz I used c#,

May I have your comments?

4

$FuncLibIn gams_fun mylib/gamsfun

the dll file is “gamsfun.dll”

and the error is:

Problem occured when trying to load mylib/gamsfun64.ll

I don’t know why 64 is added at the end!


5

When I changed the code:

$FuncLibIn gams_fun mylib\gamsfun

I got this:

Entry not found: QueryLibrary in mylib\gamsfun.dll

again the file is not loaded properly.


6

Not sure I can be of any help if the examples and the documents are not sufficient. You can’t just put a function in a DLL and hope GAMS works with it, You have to follow a strict API to make the function visible to GAMS. The trilib examples (https://www.gams.com/24.9/testlib_ml/libhtml/testlib_trilib01.html) show this for a couple of languages with very simple function (sin/cos), so you can concentrate on the mechanics.

Good luck.

Michael

7

thank you, Micheal, for your time.

I saw the code and even your codes. I should confess GAMS is the most complicated programming languages I have ever seen! Unfortunately, it’s like decoding… even the guides don’t provide any clear explanation. I don’t know why.

When I google GAMS tutorial or sources, nothing’s found. It’s really bizarre such a great software …

anyway, Many thanks…