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How to use quadgk with Matlab coder?

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Bjørn
Bjørn on 8 Oct 2013
Commented: Bjørn on 11 Oct 2013
According to the list here: http://www.mathworks.se/help/simulink/ug/functions-supported-for-code-generation--alphabetical-list.html, quadgk is supported for code generation. I have tried exporting the following code:
%#codegen
function a = bk_testfunc(b,c)
f = @(x) exp(-x.^2).*log(x).^2;
a = quadgk(f,b,c);
but I get the error message "This kind of expression is not supported." for the @(x) part.
Quadgk does not seem to accecpt inserting a function as the first argument without the @ symbol, like
a = quadgk(exp(x),b,c);
or
a = quadgk(exp(),b,c);
I cannot find any documentation on how to use quadgk with the Coder, which is particularly frustrating since the Coder does not seem to accept the normal (@) way of calling quadgk, and quadgk does not accept to be called without the @ symbol identifying the function to be integrated.

Accepted Answer

Fred Smith
Fred Smith on 9 Oct 2013
Code generation does not support
  • Anonymous function @(x)x+2
  • Nested functions (functions with end before the end of the preceding function).
Code generation does support plain-ordinary function handles: @f
So for your example what you need is this:
function a = bk_testfunc(b,c)
a = quadgk(@f_testfunc,b,c);
end %optional end.
function fx = f_testfunc(x)
fx = exp(-x.^2).*log(x).^2;
end %optional end, needed only if you keep the preceding one.
  1 Comment
Bjørn
Bjørn on 11 Oct 2013
Thank you, and thanks to everyone else who answered my question. Now it works.

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More Answers (2)

Walter Roberson
Walter Roberson on 8 Oct 2013
function fx = f_testfunc(x)
fx = exp(-x.^2).*log(x).^2;
end
now in your quadgk call, try
%#function f_testfunc
a = quadgk('f_testfunc', b, c);
the %# line is likely necessary.
  1 Comment
Ryan Livingston
Ryan Livingston on 9 Oct 2013
The pragma:
%#function ...
is only relevant to MATLAB Compiler rather than MATLAB Coder. It provides a hint to MATLAB Compiler that a function is required to be packaged up.

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Bjørn
Bjørn on 8 Oct 2013
Thanks, but I still have problems. I have done the following: first file:
%#codegen
function a = bk_testfunc(b,c)
%#function f_testfunc
a = quadgk('f_testfunc',b,c);
second file:
%#codegen
function fx = f_testfunc(x)
fx = exp(-x.^2).*log(x).^2;
end
The Coder gives the following error message: "First input argument must be a function handle."
I have also tried putting both functions in the same file:
%#codegen
function a = bk_testfunc(b,c)
%#function f_testfunc
a = quadgk('f_testfunc',b,c);
function fx = f_testfunc(x)
fx = exp(-x.^2).*log(x).^2;
end
but this gives the following error: "Parse error: File: bk_testfunc.m Line: 9 Column: 1 This statement is incomplete." (line 9 is the line with the end statement).
An end statement after the first function gives the same error message as having the functions in separate files. end with semicolon after the first function gives the error "Parameter list for function "bk_testfunc" cannot be determined due to a syntax error in the function". So while I'm a little further, I still can't generate the code.
  2 Comments
Walter Roberson
Walter Roberson on 9 Oct 2013
If you put multiple functions in the same file, they they all have to have 'end' matching their "function" statement (as in your second function), or else none of them can have that matching "end". So add an "end" after your "a = " statement.

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