i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
1d array that is stored on this process for the transform
<em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
corresponding quantities for the input.  The <code>sign</code>
(<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
match the arguments passed when creating a plan.  Although the inputs
and outputs have different data distributions in general, it is
guaranteed that the <e