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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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25 <title>FFTW 3.3.8: Basic distributed-transpose interface</title>
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71 <a name="Basic-distributed_002dtranspose-interface"></a>
72 <div class="header">
73 <p>
74 Next: <a href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface" accesskey="n" rel="next">Advanced distributed-transpose interface</a>, Previous: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="p" rel="prev">FFTW MPI Transposes</a>, Up: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="u" rel="up">FFTW MPI Transposes</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>
75 </div>
76 <hr>
77 <a name="Basic-distributed_002dtranspose-interface-1"></a>
78 <h4 class="subsection">6.7.1 Basic distributed-transpose interface</h4>
79
80 <p>In particular, suppose that we have an <code>n0</code> by <code>n1</code> array in
81 row-major order, block-distributed across the <code>n0</code> dimension. To
82 transpose this into an <code>n1</code> by <code>n0</code> array block-distributed
83 across the <code>n1</code> dimension, we would create a plan by calling the
84 following function:
85 </p>
86 <div class="example">
87 <pre class="example">fftw_plan fftw_mpi_plan_transpose(ptrdiff_t n0, ptrdiff_t n1,
88 double *in, double *out,
89 MPI_Comm comm, unsigned flags);
90 </pre></div>
91 <a name="index-fftw_005fmpi_005fplan_005ftranspose"></a>
92
93 <p>The input and output arrays (<code>in</code> and <code>out</code>) can be the
94 same. The transpose is actually executed by calling
95 <code>fftw_execute</code> on the plan, as usual.
96 <a name="index-fftw_005fexecute-3"></a>
97 </p>
98
99 <p>The <code>flags</code> are the usual FFTW planner flags, but support
100 two additional flags: <code>FFTW_MPI_TRANSPOSED_OUT</code> and/or
101 <code>FFTW_MPI_TRANSPOSED_IN</code>. What these flags indicate, for
102 transpose plans, is that the output and/or input, respectively, are
103 <em>locally</em> transposed. That is, on each process input data is
104 normally stored as a <code>local_n0</code> by <code>n1</code> array in row-major
105 order, but for an <code>FFTW_MPI_TRANSPOSED_IN</code> plan the input data is
106 stored as <code>n1</code> by <code>local_n0</code> in row-major order. Similarly,
107 <code>FFTW_MPI_TRANSPOSED_OUT</code> means that the output is <code>n0</code> by
108 <code>local_n1</code> instead of <code>local_n1</code> by <code>n0</code>.
109 <a name="index-FFTW_005fMPI_005fTRANSPOSED_005fOUT-1"></a>
110 <a name="index-FFTW_005fMPI_005fTRANSPOSED_005fIN-1"></a>
111 </p>
112
113 <p>To determine the local size of the array on each process before and
114 after the transpose, as well as the amount of storage that must be
115 allocated, one should call <code>fftw_mpi_local_size_2d_transposed</code>,
116 just as for a 2d DFT as described in the previous section:
117 <a name="index-data-distribution-4"></a>
118 </p>
119 <div class="example">
120 <pre class="example">ptrdiff_t fftw_mpi_local_size_2d_transposed
121 (ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
122 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
123 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
124 </pre></div>
125 <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed"></a>
126
127 <p>Again, the return value is the local storage to allocate, which in
128 this case is the number of <em>real</em> (<code>double</code>) values rather
129 than complex numbers as in the previous examples.
130 </p>
131 <hr>
132 <div class="header">
133 <p>
134 Next: <a href="Advanced-distributed_002dtranspose-interface.html#Advanced-distributed_002dtranspose-interface" accesskey="n" rel="next">Advanced distributed-transpose interface</a>, Previous: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="p" rel="prev">FFTW MPI Transposes</a>, Up: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="u" rel="up">FFTW MPI Transposes</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>
135 </div>
136
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