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