[petsc-users] How to build FFTW3 interface?

[Sajid Ali]

Hi PETSc Developers,

To run an example that involves the petsc-fftw interface, I loaded both
petsc and fftw modules (linked of course to the same mpi) but the compiler
complains of having no knowledge of functions like MatCreateVecsFFTW which
happens to be defined at (in the source repo)
petsc/src/mat/impls/fft/fftw.c. I don't see a corresponding definition in
the install folder (I may be wrong, but i just did a simple grep to find
the definition of the function I'm looking for and didn't find it while it
was present in the header and example files).

>From previous threads on this list-serv I see that the developers asked
users to use --download-fftw at configure time, but for users that already
have an fftw installed, is there an option to ask petsc to build the
interfaces as well (I didn't see any such option listed either here:
https://www.mcs.anl.gov/petsc/documentation/installation.html or a variant
in spack) ?

Also, could the fftw version to download be bumped to 3.3.8 (here :
petsc/config/BuildSystem/config/packages/fftw.py) since 3.3.7 gives
erroneous results with gcc-8.

Bug in fftw-3.3.7+gcc-8 :
https://github.com/FFTW/fftw3/commit/19eeeca592f63413698f23dd02b9961f22581803


Thank You,
Sajid Ali
Applied Physics
Northwestern University
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