How can I calculate the Chi-Squared CDF if I use MATLAB C-Coder?

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Aaron Chesir
Aaron Chesir on 23 Aug 2013
My MATLAB function file calls "chi2cdf", and I need to convert the script to C. The MATLAB C-Coder tool does not support the use of chi2cdf (and also does not support the use of plain cdf, either). Do any of you know of a work-around?

Answers (1)

Mike Hosea
Mike Hosea on 11 Sep 2013
This function is now supported for code generation in R2013b.
  2 Comments
Mike Hosea
Mike Hosea on 11 Sep 2013
I have no way of knowing whether you are under a maintenance agreement or not. Many users can upgrade when new releases come out. Since you apparently cannot, note that GAMMAINC is supported, and GAMMAINC will compute what is referred to as the "regularized gamma function" here
So, you could do it this way.
function p = mychi2cdf(x,a)
p = real(gammainc(max(x,0)/2,a/2));
I don't know if you cared about the possibility of negative x, but the MAX call takes care of that possibility. The wrapping with real() is only there because the output of GAMMAINC is always complex with MATLAB Coder, and we know that the imaginary part will be zero with non-negative real inputs.

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