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author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
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cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
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cannam@127 6 Copyright (C) 2003 Matteo Frigo.
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: MPI Data Distribution Functions</title>
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cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="MPI-Data-Distribution-Functions"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 75 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> &nbsp; [<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 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="MPI-Data-Distribution-Functions-1"></a>
cannam@127 79 <h4 class="subsection">6.12.4 MPI Data Distribution Functions</h4>
cannam@127 80
cannam@127 81 <a name="index-data-distribution-5"></a>
cannam@127 82 <p>As described above (see <a href="MPI-Data-Distribution.html#MPI-Data-Distribution">MPI Data Distribution</a>), in order to
cannam@127 83 allocate your arrays, <em>before</em> creating a plan, you must first
cannam@127 84 call one of the following routines to determine the required
cannam@127 85 allocation size and the portion of the array locally stored on a given
cannam@127 86 process. The <code>MPI_Comm</code> communicator passed here must be
cannam@127 87 equivalent to the communicator used below for plan creation.
cannam@127 88 </p>
cannam@127 89 <p>The basic interface for multidimensional transforms consists of the
cannam@127 90 functions:
cannam@127 91 </p>
cannam@127 92 <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-2"></a>
cannam@127 93 <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d"></a>
cannam@127 94 <a name="index-fftw_005fmpi_005flocal_005fsize"></a>
cannam@127 95 <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed-1"></a>
cannam@127 96 <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d_005ftransposed-1"></a>
cannam@127 97 <a name="index-fftw_005fmpi_005flocal_005fsize_005ftransposed"></a>
cannam@127 98 <div class="example">
cannam@127 99 <pre class="example">ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
cannam@127 100 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127 101 ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
cannam@127 102 MPI_Comm comm,
cannam@127 103 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127 104 ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm,
cannam@127 105 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127 106
cannam@127 107 ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
cannam@127 108 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127 109 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127 110 ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
cannam@127 111 MPI_Comm comm,
cannam@127 112 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127 113 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127 114 ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm,
cannam@127 115 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127 116 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127 117 </pre></div>
cannam@127 118
cannam@127 119 <p>These functions return the number of elements to allocate (complex
cannam@127 120 numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
cannam@127 121 the <code>local_n0</code> and <code>local_0_start</code> return the portion
cannam@127 122 (<code>local_0_start</code> to <code>local_0_start + local_n0 - 1</code>) of the
cannam@127 123 first dimension of an n<sub>0</sub>&nbsp;&times;&nbsp;n<sub>1</sub>&nbsp;&times;&nbsp;n<sub>2</sub>&nbsp;&times;&nbsp;&hellip;&nbsp;&times;&nbsp;n<sub>d-1</sub> array that is stored on the local
cannam@127 124 process. See <a href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a>. For
cannam@127 125 <code>FFTW_MPI_TRANSPOSED_OUT</code> plans, the &lsquo;<samp>_transposed</samp>&rsquo; variants
cannam@127 126 are useful in order to also return the local portion of the first
cannam@127 127 dimension in the n<sub>1</sub>&nbsp;&times;&nbsp;n<sub>0</sub>&nbsp;&times;&nbsp;n<sub>2</sub>&nbsp;&times;&hellip;&times;&nbsp;n<sub>d-1</sub> transposed output.
cannam@127 128 See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
cannam@127 129 The advanced interface for multidimensional transforms is:
cannam@127 130 </p>
cannam@127 131 <a name="index-advanced-interface-5"></a>
cannam@127 132 <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany-1"></a>
cannam@127 133 <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005ftransposed-1"></a>
cannam@127 134 <div class="example">
cannam@127 135 <pre class="example">ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
cannam@127 136 ptrdiff_t block0, MPI_Comm comm,
cannam@127 137 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
cannam@127 138 ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
cannam@127 139 ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm,
cannam@127 140 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
cannam@127 141 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
cannam@127 142 </pre></div>
cannam@127 143
cannam@127 144 <p>These differ from the basic interface in only two ways. First, they
cannam@127 145 allow you to specify block sizes <code>block0</code> and <code>block1</code> (the
cannam@127 146 latter for the transposed output); you can pass
cannam@127 147 <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW&rsquo;s default block size as in
cannam@127 148 the basic interface. Second, you can pass a <code>howmany</code> parameter,
cannam@127 149 corresponding to the advanced planning interface below: this is for
cannam@127 150 transforms of contiguous <code>howmany</code>-tuples of numbers
cannam@127 151 (<code>howmany = 1</code> in the basic interface).
cannam@127 152 </p>
cannam@127 153 <p>The corresponding basic and advanced routines for one-dimensional
cannam@127 154 transforms (currently only complex DFTs) are:
cannam@127 155 </p>
cannam@127 156 <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d-1"></a>
cannam@127 157 <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005f1d"></a>
cannam@127 158 <div class="example">
cannam@127 159 <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(
cannam@127 160 ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags,
cannam@127 161 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
cannam@127 162 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
cannam@127 163 ptrdiff_t fftw_mpi_local_size_many_1d(
cannam@127 164 ptrdiff_t n0, ptrdiff_t howmany,
cannam@127 165 MPI_Comm comm, int sign, unsigned flags,
cannam@127 166 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
cannam@127 167 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
cannam@127 168 </pre></div>
cannam@127 169
cannam@127 170 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT-1"></a>
cannam@127 171 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN-1"></a>
cannam@127 172 <p>As above, the return value is the number of elements to allocate
cannam@127 173 (complex numbers, for complex DFTs). The <code>local_ni</code> and
cannam@127 174 <code>local_i_start</code> arguments return the portion
cannam@127 175 (<code>local_i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
cannam@127 176 1d array that is stored on this process for the transform
cannam@127 177 <em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
cannam@127 178 corresponding quantities for the input. The <code>sign</code>
cannam@127 179 (<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
cannam@127 180 match the arguments passed when creating a plan. Although the inputs
cannam@127 181 and outputs have different data distributions in general, it is
cannam@127 182 guaranteed that the <em>output</em> data distribution of an
cannam@127 183 <code>FFTW_FORWARD</code> plan will match the <em>input</em> data distribution
cannam@127 184 of an <code>FFTW_BACKWARD</code> plan and vice versa; similarly for the
cannam@127 185 <code>FFTW_MPI_SCRAMBLED_OUT</code> and <code>FFTW_MPI_SCRAMBLED_IN</code> flags.
cannam@127 186 See <a href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>.
cannam@127 187 </p>
cannam@127 188 <hr>
cannam@127 189 <div class="header">
cannam@127 190 <p>
cannam@127 191 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> &nbsp; [<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@127 192 </div>
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