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1 <html lang="en">
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2 <head>
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3 <title>MPI Data Distribution Functions - FFTW 3.3.3</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.3.3">
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6 <meta name="generator" content="makeinfo 4.13">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="FFTW-MPI-Reference.html#FFTW-MPI-Reference" title="FFTW MPI Reference">
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9 <link rel="prev" href="Using-MPI-Plans.html#Using-MPI-Plans" title="Using MPI Plans">
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10 <link rel="next" href="MPI-Plan-Creation.html#MPI-Plan-Creation" title="MPI Plan Creation">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.3.3, 25 November 2012).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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33 -->
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34 <meta http-equiv="Content-Style-Type" content="text/css">
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35 <style type="text/css"><!--
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44 span.sansserif { font-family:sans-serif; font-weight:normal; }
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <a name="MPI-Data-Distribution-Functions"></a>
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50 <p>
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51 Next: <a rel="next" accesskey="n" href="MPI-Plan-Creation.html#MPI-Plan-Creation">MPI Plan Creation</a>,
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52 Previous: <a rel="previous" accesskey="p" href="Using-MPI-Plans.html#Using-MPI-Plans">Using MPI Plans</a>,
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53 Up: <a rel="up" accesskey="u" href="FFTW-MPI-Reference.html#FFTW-MPI-Reference">FFTW MPI Reference</a>
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54 <hr>
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55 </div>
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56
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57 <h4 class="subsection">6.12.4 MPI Data Distribution Functions</h4>
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58
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59 <p><a name="index-data-distribution-447"></a>As described above (see <a href="MPI-Data-Distribution.html#MPI-Data-Distribution">MPI Data Distribution</a>), in order to
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60 allocate your arrays, <em>before</em> creating a plan, you must first
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61 call one of the following routines to determine the required
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62 allocation size and the portion of the array locally stored on a given
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63 process. The <code>MPI_Comm</code> communicator passed here must be
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64 equivalent to the communicator used below for plan creation.
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65
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66 <p>The basic interface for multidimensional transforms consists of the
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67 functions:
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68
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69 <p><a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-448"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005f3d-449"></a><a name="index-fftw_005fmpi_005flocal_005fsize-450"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed-451"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005f3d_005ftransposed-452"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005ftransposed-453"></a>
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70 <pre class="example"> ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
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71 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
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72 ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
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73 MPI_Comm comm,
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74 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
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75 ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm,
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76 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
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77
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78 ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
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79 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
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80 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
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81 ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
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82 MPI_Comm comm,
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83 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
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84 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
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85 ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm,
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86 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
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87 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
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88 </pre>
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89 <p>These functions return the number of elements to allocate (complex
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90 numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
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91 the <code>local_n0</code> and <code>local_0_start</code> return the portion
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92 (<code>local_0_start</code> to <code>local_0_start + local_n0 - 1</code>) of the
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93 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
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94 process. See <a href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a>. For
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95 <code>FFTW_MPI_TRANSPOSED_OUT</code> plans, the ‘<samp><span class="samp">_transposed</span></samp>’ variants
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96 are useful in order to also return the local portion of the first
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97 dimension in the n<sub>1</sub> × n<sub>0</sub> × n<sub>2</sub> ×…× n<sub>d-1</sub> transposed output. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>. The advanced interface for multidimensional
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98 transforms is:
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99
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100 <p><a name="index-advanced-interface-454"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005fmany-455"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005ftransposed-456"></a>
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101 <pre class="example"> ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
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102 ptrdiff_t block0, MPI_Comm comm,
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103 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
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104 ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
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105 ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm,
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106 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
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107 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
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108 </pre>
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109 <p>These differ from the basic interface in only two ways. First, they
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110 allow you to specify block sizes <code>block0</code> and <code>block1</code> (the
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111 latter for the transposed output); you can pass
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112 <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW's default block size as in
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113 the basic interface. Second, you can pass a <code>howmany</code> parameter,
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114 corresponding to the advanced planning interface below: this is for
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115 transforms of contiguous <code>howmany</code>-tuples of numbers
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116 (<code>howmany = 1</code> in the basic interface).
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117
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118 <p>The corresponding basic and advanced routines for one-dimensional
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119 transforms (currently only complex DFTs) are:
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120
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121 <p><a name="index-fftw_005fmpi_005flocal_005fsize_005f1d-457"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005f1d-458"></a>
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122 <pre class="example"> ptrdiff_t fftw_mpi_local_size_1d(
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123 ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags,
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124 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
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125 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
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126 ptrdiff_t fftw_mpi_local_size_many_1d(
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127 ptrdiff_t n0, ptrdiff_t howmany,
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128 MPI_Comm comm, int sign, unsigned flags,
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129 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
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130 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
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131 </pre>
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132 <p><a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT-459"></a><a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN-460"></a>As above, the return value is the number of elements to allocate
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133 (complex numbers, for complex DFTs). The <code>local_ni</code> and
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134 <code>local_i_start</code> arguments return the portion
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135 (<code>local_i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
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136 1d array that is stored on this process for the transform
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137 <em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
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138 corresponding quantities for the input. The <code>sign</code>
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139 (<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
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140 match the arguments passed when creating a plan. Although the inputs
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141 and outputs have different data distributions in general, it is
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142 guaranteed that the <em>output</em> data distribution of an
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143 <code>FFTW_FORWARD</code> plan will match the <em>input</em> data distribution
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144 of an <code>FFTW_BACKWARD</code> plan and vice versa; similarly for the
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145 <code>FFTW_MPI_SCRAMBLED_OUT</code> and <code>FFTW_MPI_SCRAMBLED_IN</code> flags.
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146 See <a href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>.
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147
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148 </body></html>
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149
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