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author Chris Cannam <cannam@all-day-breakfast.com>
date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>MPI Data Distribution Functions - FFTW 3.3.3</title>
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49 <a name="MPI-Data-Distribution-Functions"></a>
50 <p>
51 Next:&nbsp;<a rel="next" accesskey="n" href="MPI-Plan-Creation.html#MPI-Plan-Creation">MPI Plan Creation</a>,
52 Previous:&nbsp;<a rel="previous" accesskey="p" href="Using-MPI-Plans.html#Using-MPI-Plans">Using MPI Plans</a>,
53 Up:&nbsp;<a rel="up" accesskey="u" href="FFTW-MPI-Reference.html#FFTW-MPI-Reference">FFTW MPI Reference</a>
54 <hr>
55 </div>
56
57 <h4 class="subsection">6.12.4 MPI Data Distribution Functions</h4>
58
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
60 allocate your arrays, <em>before</em> creating a plan, you must first
61 call one of the following routines to determine the required
62 allocation size and the portion of the array locally stored on a given
63 process. The <code>MPI_Comm</code> communicator passed here must be
64 equivalent to the communicator used below for plan creation.
65
66 <p>The basic interface for multidimensional transforms consists of the
67 functions:
68
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>
70 <pre class="example"> ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
71 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
72 ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
73 MPI_Comm comm,
74 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
75 ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm,
76 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
77
78 ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
79 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
80 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
81 ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
82 MPI_Comm comm,
83 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
84 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
85 ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm,
86 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
87 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
88 </pre>
89 <p>These functions return the number of elements to allocate (complex
90 numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
91 the <code>local_n0</code> and <code>local_0_start</code> return the portion
92 (<code>local_0_start</code> to <code>local_0_start + local_n0 - 1</code>) of the
93 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
94 process. See <a href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a>. For
95 <code>FFTW_MPI_TRANSPOSED_OUT</code> plans, the &lsquo;<samp><span class="samp">_transposed</span></samp>&rsquo; variants
96 are useful in order to also return the local portion of the first
97 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. See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>. The advanced interface for multidimensional
98 transforms is:
99
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>
101 <pre class="example"> ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
102 ptrdiff_t block0, MPI_Comm comm,
103 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
104 ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
105 ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm,
106 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
107 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
108 </pre>
109 <p>These differ from the basic interface in only two ways. First, they
110 allow you to specify block sizes <code>block0</code> and <code>block1</code> (the
111 latter for the transposed output); you can pass
112 <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW's default block size as in
113 the basic interface. Second, you can pass a <code>howmany</code> parameter,
114 corresponding to the advanced planning interface below: this is for
115 transforms of contiguous <code>howmany</code>-tuples of numbers
116 (<code>howmany = 1</code> in the basic interface).
117
118 <p>The corresponding basic and advanced routines for one-dimensional
119 transforms (currently only complex DFTs) are:
120
121 <p><a name="index-fftw_005fmpi_005flocal_005fsize_005f1d-457"></a><a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005f1d-458"></a>
122 <pre class="example"> ptrdiff_t fftw_mpi_local_size_1d(
123 ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags,
124 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
125 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
126 ptrdiff_t fftw_mpi_local_size_many_1d(
127 ptrdiff_t n0, ptrdiff_t howmany,
128 MPI_Comm comm, int sign, unsigned flags,
129 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
130 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
131 </pre>
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
133 (complex numbers, for complex DFTs). The <code>local_ni</code> and
134 <code>local_i_start</code> arguments return the portion
135 (<code>local_i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
136 1d array that is stored on this process for the transform
137 <em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
138 corresponding quantities for the input. The <code>sign</code>
139 (<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
140 match the arguments passed when creating a plan. Although the inputs
141 and outputs have different data distributions in general, it is
142 guaranteed that the <em>output</em> data distribution of an
143 <code>FFTW_FORWARD</code> plan will match the <em>input</em> data distribution
144 of an <code>FFTW_BACKWARD</code> plan and vice versa; similarly for the
145 <code>FFTW_MPI_SCRAMBLED_OUT</code> and <code>FFTW_MPI_SCRAMBLED_IN</code> flags.
146 See <a href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>.
147
148 </body></html>
149