Hello Likun, Regarding your question sent 5 days ago. I think you can have a overview of all the examples under the directory src/mat/examples/tests/ following the link: http://www.mcs.anl.gov/petsc/petsc-current/src/mat/examples/tests/
Among these examples, there are 14 about fftw, and there are some with mpi FFTW, for instance, ex143, 144, 146, 158, etc. If you take a look at these examples, you will find that they are using another package FFTW3 as well as the interface between FFTW3 and PETSc. In fact, if you download and install FFTW3 with the right configuration, you should be able to do FFT in parallel without PETSc. If you want to do FFT in parallel in PETSc, you may have to figure out more from those examples provided. Best, Hui
