[Users] fftw and MKL

Roland Haas rhaas at illinois.edu
Mon Oct 22 14:06:47 CDT 2018


Hello Yosef,

>    I got bitten by an issue regarding the link order. I use  fftw3 for a 
> series of transforms of a type not supported by the MKL fftw wrapper 
> (r2r transforms). I have FFTW3 either built, or use a prebuilt version. 
> The issue comes up if mkl precedes fftw3 on the link line. If it does, 
> then rather than using fftw functions, mkl functions are used instead 
> (and these always fail).
> 
> See r2r transforms here:
> https://software.intel.com/en-us/mkl-developer-reference-c-using-fftw3-wrappers
> 
> Since MKL does not support the functions I need, is there a way to force 
> -mkl to always occur only after -lfftw3 on the link line?
You could try making the thorn that adds -mkl REQUIRE FFTW3 which
enforces a link order and (hopefully) fixes the issue.

Or, and this may be better, put a LIBS line in to your option list that
lists -mkl and fftw3 in the correct order (though of course -mkl is
"special" and the compiler may not do what you think it should do).

Yours,
Roland

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