Modelica Forum > Functions with variable size inputs

Full Version: Functions with variable size inputs

Lars

Dec 18 2006, 09:14 AM

Consider the following test function, and test usage:

CODE

function testfun
  parameter Integer n = size(a,1);
  input Real[n] a;
  output Real[n] b;
algorithm
  b := 2*a;
end testfun;

model testmod
  Real[2] a;
  Real[2] b;
equation
  b = {1,2};
  a = testfun(b);
end testmod;

The function can be checked (in Dymola) without errors, but when I check the model, I get

QUOTE

Error: Unknown variable n in size expression: n
for function Test.testfun
Errors or failure to expand the equation:
equation
a = Test.testfun(b);
Found in class Test.testmod, declaration window at line 6.

The usage of the parameter n is inspired from the example at page 303 (bottom) in Fritzon's book.

For this simple test example, I know that the code below would work. However, (I think) I really need to know the input sizes in defining outputs in the function where I have this problem. Compare for example if a in the model above is defines as Real[:] (which is still not the same error message I get, but similar).

CODE

function testfun
  input Real[:] a;
  output Real[:] b;
algorithm
  b := 2*a;
end testfun;

wagner

Dec 18 2006, 11:11 AM

Hello Lars,

the following code for your test function runs on Dymola 6.0b. Maybe it solves the problem you have.

CODE

function testfun
  input Real[:] a;
  output Real[size(a,1)] b;

algorithm
  b := 2*a;
end testfun;

The workaround with parameter does not seem to work on the current versions of dymola.

Regards

Florian

Lars

Dec 18 2006, 02:29 PM

Many thanks, this does solve my problem.

It seems there is an error in either Dymola or Fritzson's book.

Lars

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