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cannam@127: <title>FFTW 3.3.5: MPI Data Distribution Functions</title>
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cannam@127: <a name="MPI-Data-Distribution-Functions"></a>
cannam@127: <div class="header">
cannam@127: <p>
cannam@127: 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>
cannam@127: </div>
cannam@127: <hr>
cannam@127: <a name="MPI-Data-Distribution-Functions-1"></a>
cannam@127: <h4 class="subsection">6.12.4 MPI Data Distribution Functions</h4>
cannam@127:
cannam@127: <a name="index-data-distribution-5"></a>
cannam@127: <p>As described above (see <a href="MPI-Data-Distribution.html#MPI-Data-Distribution">MPI Data Distribution</a>), in order to
cannam@127: allocate your arrays, <em>before</em> creating a plan, you must first
cannam@127: call one of the following routines to determine the required
cannam@127: allocation size and the portion of the array locally stored on a given
cannam@127: process. The <code>MPI_Comm</code> communicator passed here must be
cannam@127: equivalent to the communicator used below for plan creation.
cannam@127: </p>
cannam@127: <p>The basic interface for multidimensional transforms consists of the
cannam@127: functions:
cannam@127: </p>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-2"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed-1"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d_005ftransposed-1"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005ftransposed"></a>
cannam@127: <div class="example">
cannam@127: <pre class="example">ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127: ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
cannam@127: MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127: ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127:
cannam@127: ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127: ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
cannam@127: MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127: ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127: </pre></div>
cannam@127:
cannam@127: <p>These functions return the number of elements to allocate (complex
cannam@127: numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
cannam@127: the <code>local_n0</code> and <code>local_0_start</code> return the portion
cannam@127: (<code>local_0_start</code> to <code>local_0_start + local_n0 - 1</code>) of the
cannam@127: 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
cannam@127: process. See <a href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a>. For
cannam@127: <code>FFTW_MPI_TRANSPOSED_OUT</code> plans, the ‘<samp>_transposed</samp>’ variants
cannam@127: are useful in order to also return the local portion of the first
cannam@127: dimension in the n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> transposed output.
cannam@127: See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
cannam@127: The advanced interface for multidimensional transforms is:
cannam@127: </p>
cannam@127: <a name="index-advanced-interface-5"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany-1"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005ftransposed-1"></a>
cannam@127: <div class="example">
cannam@127: <pre class="example">ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
cannam@127: ptrdiff_t block0, MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127: ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
cannam@127: ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm,
cannam@127: ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127: ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127: </pre></div>
cannam@127:
cannam@127: <p>These differ from the basic interface in only two ways. First, they
cannam@127: allow you to specify block sizes <code>block0</code> and <code>block1</code> (the
cannam@127: latter for the transposed output); you can pass
cannam@127: <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW’s default block size as in
cannam@127: the basic interface. Second, you can pass a <code>howmany</code> parameter,
cannam@127: corresponding to the advanced planning interface below: this is for
cannam@127: transforms of contiguous <code>howmany</code>-tuples of numbers
cannam@127: (<code>howmany = 1</code> in the basic interface).
cannam@127: </p>
cannam@127: <p>The corresponding basic and advanced routines for one-dimensional
cannam@127: transforms (currently only complex DFTs) are:
cannam@127: </p>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d-1"></a>
cannam@127: <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005f1d"></a>
cannam@127: <div class="example">
cannam@127: <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(
cannam@127: ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags,
cannam@127: ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
cannam@127: ptrdiff_t *local_no, ptrdiff_t *local_o_start);
cannam@127: ptrdiff_t fftw_mpi_local_size_many_1d(
cannam@127: ptrdiff_t n0, ptrdiff_t howmany,
cannam@127: MPI_Comm comm, int sign, unsigned flags,
cannam@127: ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
cannam@127: ptrdiff_t *local_no, ptrdiff_t *local_o_start);
cannam@127: </pre></div>
cannam@127:
cannam@127: <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT-1"></a>
cannam@127: <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN-1"></a>
cannam@127: <p>As above, the return value is the number of elements to allocate
cannam@127: (complex numbers, for complex DFTs). The <code>local_ni</code> and
cannam@127: <code>local_i_start</code> arguments return the portion
cannam@127: (<code>local_i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
cannam@127: 1d array that is stored on this process for the transform
cannam@127: <em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
cannam@127: corresponding quantities for the input. The <code>sign</code>
cannam@127: (<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
cannam@127: match the arguments passed when creating a plan. Although the inputs
cannam@127: and outputs have different data distributions in general, it is
cannam@127: guaranteed that the <em>output</em> data distribution of an
cannam@127: <code>FFTW_FORWARD</code> plan will match the <em>input</em> data distribution
cannam@127: of an <code>FFTW_BACKWARD</code> plan and vice versa; similarly for the
cannam@127: <code>FFTW_MPI_SCRAMBLED_OUT</code> and <code>FFTW_MPI_SCRAMBLED_IN</code> flags.
cannam@127: See <a href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>.
cannam@127: </p>
cannam@127: <hr>
cannam@127: <div class="header">
cannam@127: <p>
cannam@127: 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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