MPI FFTW in Fortran for a 3D complex array

Question

I need to make a FFT of a 3D array in Fortran using MPI. I've been looking at the FFTW website and I also tried to look for examples online but I could find only this code:

   use, intrinsic :: iso_c_binding
   include 'fftw3-mpi.f03'
   integer(C_INTPTR_T), parameter :: L = ...
   integer(C_INTPTR_T), parameter :: M = ...
   type(C_PTR) :: plan, cdata
   complex(C_DOUBLE_COMPLEX), pointer :: data(:,:)
   integer(C_INTPTR_T) :: i, j, alloc_local, local_M, local_j_offset

 !   get local data size and allocate (note dimension reversal)
   alloc_local = fftw_mpi_local_size_2d(M, L, MPI_COMM_WORLD, &
                                        local_M, local_j_offset)
   cdata = fftw_alloc_complex(alloc_local)
   call c_f_pointer(cdata, data, [L,local_M])

 !   create MPI plan for in-place forward DFT (note dimension reversal)
   plan = fftw_mpi_plan_dft_2d(M, L, data, data, MPI_COMM_WORLD, &
                               FFTW_FORWARD, FFTW_MEASURE)

 ! initialize data to some function my_function(i,j)
   do j = 1, local_M
     do i = 1, L
       data(i, j) = my_function(i, j + local_j_offset)
     end do
   end do

 ! compute transform (as many times as desired)
   call fftw_mpi_execute_dft(plan, data, data)

   call fftw_destroy_plan(plan)
   call fftw_free(cdata)

This code computes the FFT transform of a 2d array. My question is: how can I use this code to compute a FFT transform of a 3d array?

Answer 1

Regarding fftw_mpi_plan_dft_2d have a look at:

http://www.fftw.org/doc/MPI-Plan-Creation.html

It is quite obvious that there must be a fftw_mpi_plan_dft_3d function as well. The same of course for fftw_mpi_local_size_2d. The arguments will change slightly but the documentation will help you on this.