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), 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. 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