Trying to include an external dll (compiled from c)

Posted 14 janv. 2024, 11:15 UTC−5 API, Modeling Workflow, User Interface Version 6.2 3 Replies

Maximilian Hohenberger

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Hello,

I am trying to use a custom function in comsol. For testing purposes, I have written a short c file:

double f(double x, double y, double z);

double f(double x, double y, double z) {

    double r;

    r = x * (1 + 1*(y-z) + 1*(y-z));

    return r;
}

Then I compiled my code as adviced on suggested on cygwin with the commands gcc -c test.c and then gcc -shared -o test.dll test.o.

Now in Global Definitions, I created a new instance with right click -> functions -> extern, filled out function name with "f" and arguments with "x, y, z" and finally created 3 entries in plot parameters ranging from 0 to 10 for every entry.

Now if I click "plot" or "create plot" I get an error saying "Symbol not found". I have googled and asked Bing "to google for me" but I dont find any resource that helps me here.

How do I make this work?

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3 Replies Last Post 16 janv. 2024, 10:07 UTC−5

Magnus Ringh COMSOL Employee

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Posted: 4 months ago

Hi Maximilian,

For an external function in COMSOL Multiphysics, you must define three functions: init, eval, and getLastError, and for the numerical evaluation, the input and output arguments must be arrays (x, y, and z in your example and in general are numerical arrays). See the COMSOL Multiphysics Programming Reference Manual for more information and an example.

Best regards,

Magnus

Maximilian Hohenberger

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Posted: 4 months ago

Hi Maximilian,

For an external function in COMSOL Multiphysics, you must define three functions: init, eval, and getLastError, and for the numerical evaluation, the input and output arguments must be arrays (x, y, and z in your example and in general are numerical arrays). See the COMSOL Multiphysics Programming Reference Manual for more information and an example.

Best regards,

Magnus

Thank you for your anwser. Could you tell me where exactly you found the example in the manual? I search for a bit, but couln't locate it.

Magnus Ringh COMSOL Employee

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Posted: 4 months ago

Thank you for your anwser. Could you tell me where exactly you found the example in the manual? I search for a bit, but couln't locate it.

Hi Maximilian,

It's located in the COMSOL Multiphysics Programming Reference Manual, under General Commands>About General Commands>model.func(). Then scroll down to External.

Best regards,

Magnus

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