Once an MPI plan is created, you can execute and destroy it using
fftw_execute, fftw_destroy_plan, and the other functions
in the serial interface that operate on generic plans (see Using Plans).
The fftw_execute and fftw_destroy_plan functions, applied to
MPI plans, are collective calls: they must be called for all processes
in the communicator that was used to create the plan.
You must not use the serial new-array plan-execution functions
fftw_execute_dft and so on (see New-array Execute Functions) with MPI plans. Such functions are specialized to the
problem type, and there are specific new-array execute functions for MPI plans:
void fftw_mpi_execute_dft(fftw_plan p, fftw_complex *in, fftw_complex *out);
void fftw_mpi_execute_dft_r2c(fftw_plan p, double *in, fftw_complex *out);
void fftw_mpi_execute_dft_c2r(fftw_plan p, fftw_complex *in, double *out);
void fftw_mpi_execute_r2r(fftw_plan p, double *in, double *out);
These functions have the same restrictions as those of the serial
new-array execute functions. They are always safe to apply to
the same in and out arrays that were used to
create the plan. They can only be applied to new arrarys if those
arrays have the same types, dimensions, in-placeness, and alignment as
the original arrays, where the best way to ensure the same alignment
is to use FFTW's fftw_malloc and related allocation functions
for all arrays (see Memory Allocation). Note that distributed
transposes (see FFTW MPI Transposes) use
fftw_mpi_execute_r2r, since they count as rank-zero r2r plans
from FFTW's perspective.