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<h4 class="subsection">6.12.3 Using MPI Plans</h4>

<p>Once an MPI plan is created, you can execute and destroy it using
<code>fftw_execute</code>, <code>fftw_destroy_plan</code>, and the other functions
in the serial interface that operate on generic plans (see <a href="Using-Plans.html#Using-Plans">Using Plans</a>).

   <p><a name="index-collective-function-438"></a><a name="index-MPI-communicator-439"></a>The <code>fftw_execute</code> and <code>fftw_destroy_plan</code> functions, applied to
MPI plans, are <em>collective</em> calls: they must be called for all processes
in the communicator that was used to create the plan.

   <p><a name="index-new_002darray-execution-440"></a>You must <em>not</em> use the serial new-array plan-execution functions
<code>fftw_execute_dft</code> and so on (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>) with MPI plans.  Such functions are specialized to the
problem type, and there are specific new-array execute functions for MPI plans:

   <p><a name="index-fftw_005fmpi_005fexecute_005fdft-441"></a><a name="index-fftw_005fmpi_005fexecute_005fdft_005fr2c-442"></a><a name="index-fftw_005fmpi_005fexecute_005fdft_005fc2r-443"></a><a name="index-fftw_005fmpi_005fexecute_005fr2r-444"></a>
<pre class="example">     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);
</pre>
   <p><a name="index-alignment-445"></a><a name="index-fftw_005fmalloc-446"></a>These functions have the same restrictions as those of the serial
new-array execute functions.  They are <em>always</em> safe to apply to
the <em>same</em> <code>in</code> and <code>out</code> 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 <code>fftw_malloc</code> and related allocation functions
for all arrays (see <a href="Memory-Allocation.html#Memory-Allocation">Memory Allocation</a>).  Note that distributed
transposes (see <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes">FFTW MPI Transposes</a>) use
<code>fftw_mpi_execute_r2r</code>, since they count as rank-zero r2r plans
from FFTW's perspective.

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author	Chris Cannam
date	Wed, 20 Mar 2013 15:35:50 +0000
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