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Chris@42: <title>FFTW 3.3.5: MPI Data Distribution Functions</title>
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Chris@42: <a name="MPI-Data-Distribution-Functions"></a>
Chris@42: <div class="header">
Chris@42: <p>
Chris@42: Next: <a href="MPI-Plan-Creation.html#MPI-Plan-Creation" accesskey="n" rel="next">MPI Plan Creation</a>, Previous: <a href="Using-MPI-Plans.html#Using-MPI-Plans" accesskey="p" rel="prev">Using MPI Plans</a>, Up: <a href="FFTW-MPI-Reference.html#FFTW-MPI-Reference" accesskey="u" rel="up">FFTW MPI Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@42: </div>
Chris@42: <hr>
Chris@42: <a name="MPI-Data-Distribution-Functions-1"></a>
Chris@42: <h4 class="subsection">6.12.4 MPI Data Distribution Functions</h4>
Chris@42:
Chris@42: <a name="index-data-distribution-5"></a>
Chris@42: <p>As described above (see <a href="MPI-Data-Distribution.html#MPI-Data-Distribution">MPI Data Distribution</a>), in order to
Chris@42: allocate your arrays, <em>before</em> creating a plan, you must first
Chris@42: call one of the following routines to determine the required
Chris@42: allocation size and the portion of the array locally stored on a given
Chris@42: process. The <code>MPI_Comm</code> communicator passed here must be
Chris@42: equivalent to the communicator used below for plan creation.
Chris@42: </p>
Chris@42: <p>The basic interface for multidimensional transforms consists of the
Chris@42: functions:
Chris@42: </p>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-2"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed-1"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d_005ftransposed-1"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005ftransposed"></a>
Chris@42: <div class="example">
Chris@42: <pre class="example">ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
Chris@42: ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
Chris@42: MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
Chris@42: ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
Chris@42:
Chris@42: ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
Chris@42: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
Chris@42: ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
Chris@42: MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
Chris@42: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
Chris@42: ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
Chris@42: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
Chris@42: </pre></div>
Chris@42:
Chris@42: <p>These functions return the number of elements to allocate (complex
Chris@42: numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
Chris@42: the <code>local_n0</code> and <code>local_0_start</code> return the portion
Chris@42: (<code>local_0_start</code> to <code>local_0_start + local_n0 - 1</code>) of the
Chris@42: first dimension of an n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub> array that is stored on the local
Chris@42: process. See <a href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a>. For
Chris@42: <code>FFTW_MPI_TRANSPOSED_OUT</code> plans, the ‘<samp>_transposed</samp>’ variants
Chris@42: are useful in order to also return the local portion of the first
Chris@42: dimension in the n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> transposed output.
Chris@42: See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
Chris@42: The advanced interface for multidimensional transforms is:
Chris@42: </p>
Chris@42: <a name="index-advanced-interface-5"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany-1"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005ftransposed-1"></a>
Chris@42: <div class="example">
Chris@42: <pre class="example">ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
Chris@42: ptrdiff_t block0, MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
Chris@42: ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
Chris@42: ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm,
Chris@42: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
Chris@42: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
Chris@42: </pre></div>
Chris@42:
Chris@42: <p>These differ from the basic interface in only two ways. First, they
Chris@42: allow you to specify block sizes <code>block0</code> and <code>block1</code> (the
Chris@42: latter for the transposed output); you can pass
Chris@42: <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW’s default block size as in
Chris@42: the basic interface. Second, you can pass a <code>howmany</code> parameter,
Chris@42: corresponding to the advanced planning interface below: this is for
Chris@42: transforms of contiguous <code>howmany</code>-tuples of numbers
Chris@42: (<code>howmany = 1</code> in the basic interface).
Chris@42: </p>
Chris@42: <p>The corresponding basic and advanced routines for one-dimensional
Chris@42: transforms (currently only complex DFTs) are:
Chris@42: </p>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d-1"></a>
Chris@42: <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005f1d"></a>
Chris@42: <div class="example">
Chris@42: <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(
Chris@42: ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags,
Chris@42: ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
Chris@42: ptrdiff_t *local_no, ptrdiff_t *local_o_start);
Chris@42: ptrdiff_t fftw_mpi_local_size_many_1d(
Chris@42: ptrdiff_t n0, ptrdiff_t howmany,
Chris@42: MPI_Comm comm, int sign, unsigned flags,
Chris@42: ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
Chris@42: ptrdiff_t *local_no, ptrdiff_t *local_o_start);
Chris@42: </pre></div>
Chris@42:
Chris@42: <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT-1"></a>
Chris@42: <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN-1"></a>
Chris@42: <p>As above, the return value is the number of elements to allocate
Chris@42: (complex numbers, for complex DFTs). The <code>local_ni</code> and
Chris@42: <code>local_i_start</code> arguments return the portion
Chris@42: (<code>local_i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
Chris@42: 1d array that is stored on this process for the transform
Chris@42: <em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
Chris@42: corresponding quantities for the input. The <code>sign</code>
Chris@42: (<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
Chris@42: match the arguments passed when creating a plan. Although the inputs
Chris@42: and outputs have different data distributions in general, it is
Chris@42: guaranteed that the <em>output</em> data distribution of an
Chris@42: <code>FFTW_FORWARD</code> plan will match the <em>input</em> data distribution
Chris@42: of an <code>FFTW_BACKWARD</code> plan and vice versa; similarly for the
Chris@42: <code>FFTW_MPI_SCRAMBLED_OUT</code> and <code>FFTW_MPI_SCRAMBLED_IN</code> flags.
Chris@42: See <a href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>.
Chris@42: </p>
Chris@42: <hr>
Chris@42: <div class="header">
Chris@42: <p>
Chris@42: Next: <a href="MPI-Plan-Creation.html#MPI-Plan-Creation" accesskey="n" rel="next">MPI Plan Creation</a>, Previous: <a href="Using-MPI-Plans.html#Using-MPI-Plans" accesskey="p" rel="prev">Using MPI Plans</a>, Up: <a href="FFTW-MPI-Reference.html#FFTW-MPI-Reference" accesskey="u" rel="up">FFTW MPI Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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