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25 <title>FFTW 3.3.5: MPI Data Distribution Functions</title>
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72 <a name="MPI-Data-Distribution-Functions"></a>
73 <div class="header">
74 <p>
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>
76 </div>
77 <hr>
78 <a name="MPI-Data-Distribution-Functions-1"></a>
79 <h4 class="subsection">6.12.4 MPI Data Distribution Functions</h4>
80
81 <a name="index-data-distribution-5"></a>
82 <p>As described above (see <a href="MPI-Data-Distribution.html#MPI-Data-Distribution">MPI Data Distribution</a>), in order to
83 allocate your arrays, <em>before</em> creating a plan, you must first
84 call one of the following routines to determine the required
85 allocation size and the portion of the array locally stored on a given
86 process. The <code>MPI_Comm</code> communicator passed here must be
87 equivalent to the communicator used below for plan creation.
88 </p>
89 <p>The basic interface for multidimensional transforms consists of the
90 functions:
91 </p>
92 <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d-2"></a>
93 <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d"></a>
94 <a name="index-fftw_005fmpi_005flocal_005fsize"></a>
95 <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d_005ftransposed-1"></a>
96 <a name="index-fftw_005fmpi_005flocal_005fsize_005f3d_005ftransposed-1"></a>
97 <a name="index-fftw_005fmpi_005flocal_005fsize_005ftransposed"></a>
98 <div class="example">
99 <pre class="example">ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
100 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
101 ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
102 MPI_Comm comm,
103 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
104 ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm,
105 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
106
107 ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm,
108 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
109 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
110 ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2,
111 MPI_Comm comm,
112 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
113 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
114 ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm,
115 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
116 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
117 </pre></div>
118
119 <p>These functions return the number of elements to allocate (complex
120 numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
121 the <code>local_n0</code> and <code>local_0_start</code> return the portion
122 (<code>local_0_start</code> to <code>local_0_start + local_n0 - 1</code>) of the
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
124 process. See <a href="Basic-and-advanced-distribution-interfaces.html#Basic-and-advanced-distribution-interfaces">Basic and advanced distribution interfaces</a>. For
125 <code>FFTW_MPI_TRANSPOSED_OUT</code> plans, the &lsquo;<samp>_transposed</samp>&rsquo; variants
126 are useful in order to also return the local portion of the first
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.
128 See <a href="Transposed-distributions.html#Transposed-distributions">Transposed distributions</a>.
129 The advanced interface for multidimensional transforms is:
130 </p>
131 <a name="index-advanced-interface-5"></a>
132 <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany-1"></a>
133 <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005ftransposed-1"></a>
134 <div class="example">
135 <pre class="example">ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
136 ptrdiff_t block0, MPI_Comm comm,
137 ptrdiff_t *local_n0, ptrdiff_t *local_0_start);
138 ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany,
139 ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm,
140 ptrdiff_t *local_n0, ptrdiff_t *local_0_start,
141 ptrdiff_t *local_n1, ptrdiff_t *local_1_start);
142 </pre></div>
143
144 <p>These differ from the basic interface in only two ways. First, they
145 allow you to specify block sizes <code>block0</code> and <code>block1</code> (the
146 latter for the transposed output); you can pass
147 <code>FFTW_MPI_DEFAULT_BLOCK</code> to use FFTW&rsquo;s default block size as in
148 the basic interface. Second, you can pass a <code>howmany</code> parameter,
149 corresponding to the advanced planning interface below: this is for
150 transforms of contiguous <code>howmany</code>-tuples of numbers
151 (<code>howmany = 1</code> in the basic interface).
152 </p>
153 <p>The corresponding basic and advanced routines for one-dimensional
154 transforms (currently only complex DFTs) are:
155 </p>
156 <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d-1"></a>
157 <a name="index-fftw_005fmpi_005flocal_005fsize_005fmany_005f1d"></a>
158 <div class="example">
159 <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(
160 ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags,
161 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
162 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
163 ptrdiff_t fftw_mpi_local_size_many_1d(
164 ptrdiff_t n0, ptrdiff_t howmany,
165 MPI_Comm comm, int sign, unsigned flags,
166 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
167 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
168 </pre></div>
169
170 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT-1"></a>
171 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN-1"></a>
172 <p>As above, the return value is the number of elements to allocate
173 (complex numbers, for complex DFTs). The <code>local_ni</code> and
174 <code>local_i_start</code> arguments return the portion
175 (<code>local_i_start</code> to <code>local_i_start + local_ni - 1</code>) of the
176 1d array that is stored on this process for the transform
177 <em>input</em>, and <code>local_no</code> and <code>local_o_start</code> are the
178 corresponding quantities for the input. The <code>sign</code>
179 (<code>FFTW_FORWARD</code> or <code>FFTW_BACKWARD</code>) and <code>flags</code> must
180 match the arguments passed when creating a plan. Although the inputs
181 and outputs have different data distributions in general, it is
182 guaranteed that the <em>output</em> data distribution of an
183 <code>FFTW_FORWARD</code> plan will match the <em>input</em> data distribution
184 of an <code>FFTW_BACKWARD</code> plan and vice versa; similarly for the
185 <code>FFTW_MPI_SCRAMBLED_OUT</code> and <code>FFTW_MPI_SCRAMBLED_IN</code> flags.
186 See <a href="One_002ddimensional-distributions.html#One_002ddimensional-distributions">One-dimensional distributions</a>.
187 </p>
188 <hr>
189 <div class="header">
190 <p>
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>
192 </div>
193
194
195
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