[petsc-users] Using PFFT within PETSc

[Giuseppe Pitton]

Dear Matt,
I cannot rewrite this example using the MatCreateFFT calls because it is 
not clear to me which is the shape and the ordering of the vectors 
produced by MatScatterPetscToFFTW. Furthermore, if I understand 
correctly this function returns the c2r / r2c Fourier transforms, and 
not the c2c transforms (unless PETSc is configured for complex data).
However, I have rewritten the example using FFTW instead of PFFT 
(attached), and it runs fine both in serial and in parallel (with a  cpu 
count that should be a power of two). However, I prefer using PFFT over 
FFTW, so if somebody has comments on this library, it would be great to 
know.
Thank you,
Giuseppe




On 11/23/2015 03:09 PM, Matthew Knepley wrote:
> On Mon, Nov 23, 2015 at 1:31 AM, Giuseppe Pitton <gpitton at sissa.it 
> <mailto:gpitton at sissa.it>> wrote:
>
>     Dear users and developers,
>     I am trying to interface PETSc with the parallel fast Fourier
>     transform library PFFT
>     (https://www-user.tu-chemnitz.de/~potts/workgroup/pippig/software.php.en
>     <https://www-user.tu-chemnitz.de/%7Epotts/workgroup/pippig/software.php.en>),
>     based in turn on FFTW. My plan is to build a spectral
>     differentiation code, and in the attached files you can see a
>     simple example.
>
>
> Is it possible to write this example using the existing calls?
>
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateFFT.html
>
> That way we would have a baseline we could both run that works, and 
> then we could look
> at something broken.
>
>   Thanks,
>
>      Matt
>
>     The code works correctly in serial, but in parallel there are some
>     problems regarding the output of the results, I think due to some
>     differences in the way PETSc and PFFT store data, but I'm not sure
>     if this is really the issue.
>     In the attached code, the number of processors used should be
>     specified at compile time in the variable "ncpus". As long as
>     ncpus = 1, everything works fine, but if ncpus = 2 or an higher
>     power of 2, the code terminates correctly but the results show
>     some artifacts, as you can see from the generated hdf5 file, named
>     "output-pfft.h5".
>     In the makefile the variables PFFTINC, PFFTLIB, FFTWINC and
>     FFTWLIB should be set correctly.
>     Thank you,
>     Giuseppe
>
>
>
>
> -- 
> What most experimenters take for granted before they begin their 
> experiments is infinitely more interesting than any results to which 
> their experiments lead.
> -- Norbert Wiener

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PFFTINC		 = /pfft-1.0.8/include
FFTWINC		 = /fftw-3.3.4/include
PFFTLIB		 = /pfft-1.0.8/lib
FFTWLIB		 = /fftw-3.3.4/lib

CFLAGS	         =-std=c99 -I${PFFTINC} -I${FFTWINC} -L${PFFTLIB} -L${FFTWLIB}
CLEANFILES       = output-pfft.h5 test-pfft
NP               = 1

include ${PETSC_DIR}lib/petsc/conf/variables
include ${PETSC_DIR}lib/petsc/conf/rules


test-fftw: test-fftw.o  chkopts
	-${CLINKER} -o test-fftw test-fftw.o -lm -lfftw3 -lfftw3_mpi ${PETSC_LIB}
	${RM} test-fftw.o
test-pfft: test-pfft.o  chkopts
	-${CLINKER} -o test-pfft test-pfft.o -lm -lpfft -lfftw3 -lfftw3_mpi ${PETSC_LIB}
	${RM} test-pfft.o

include ${PETSC_DIR}lib/petsc/conf/test
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