ly
more complicated because the data distribution is more closely tied to
how the algorithm works.  In particular, you can no longer pass an
arbitrary block size and must accept FFTW's default; also, the block
sizes may be different for input and output.  Also, the data
distribution depends on the flags and transform direction, in order
for forward and backward transforms to work correctly.

<pre class="example">     ptrdiff_t fftw_mpi_local_size_1d(ptrdiff_t n0, MPI_Comm comm,
                     int sign