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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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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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3 <!-- This manual is for FFTW
4 (version 3.3.8, 24 May 2018).
5
6 Copyright (C) 2003 Matteo Frigo.
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8 Copyright (C) 2003 Massachusetts Institute of Technology.
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24 <head>
25 <title>FFTW 3.3.8: One-dimensional distributions</title>
26
27 <meta name="description" content="FFTW 3.3.8: One-dimensional distributions">
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35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
36 <link href="MPI-Data-Distribution.html#MPI-Data-Distribution" rel="up" title="MPI Data Distribution">
37 <link href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html#Multi_002ddimensional-MPI-DFTs-of-Real-Data" rel="next" title="Multi-dimensional MPI DFTs of Real Data">
38 <link href="Transposed-distributions.html#Transposed-distributions" rel="prev" title="Transposed distributions">
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71 <a name="One_002ddimensional-distributions"></a>
72 <div class="header">
73 <p>
74 Previous: <a href="Transposed-distributions.html#Transposed-distributions" accesskey="p" rel="prev">Transposed distributions</a>, Up: <a href="MPI-Data-Distribution.html#MPI-Data-Distribution" accesskey="u" rel="up">MPI Data Distribution</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="One_002ddimensional-distributions-1"></a>
78 <h4 class="subsection">6.4.4 One-dimensional distributions</h4>
79
80 <p>For one-dimensional distributed DFTs using FFTW, matters are slightly
81 more complicated because the data distribution is more closely tied to
82 how the algorithm works. In particular, you can no longer pass an
83 arbitrary block size and must accept FFTW&rsquo;s default; also, the block
84 sizes may be different for input and output. Also, the data
85 distribution depends on the flags and transform direction, in order
86 for forward and backward transforms to work correctly.
87 </p>
88 <div class="example">
89 <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(ptrdiff_t n0, MPI_Comm comm,
90 int sign, unsigned flags,
91 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
92 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
93 </pre></div>
94 <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d"></a>
95
96 <p>This function computes the data distribution for a 1d transform of
97 size <code>n0</code> with the given transform <code>sign</code> and <code>flags</code>.
98 Both input and output data use block distributions. The input on the
99 current process will consist of <code>local_ni</code> numbers starting at
100 index <code>local_i_start</code>; e.g. if only a single process is used,
101 then <code>local_ni</code> will be <code>n0</code> and <code>local_i_start</code> will
102 be <code>0</code>. Similarly for the output, with <code>local_no</code> numbers
103 starting at index <code>local_o_start</code>. The return value of
104 <code>fftw_mpi_local_size_1d</code> will be the total number of elements to
105 allocate on the current process (which might be slightly larger than
106 the local size due to intermediate steps in the algorithm).
107 </p>
108 <p>As mentioned above (see <a href="Load-balancing.html#Load-balancing">Load balancing</a>), the data will be divided
109 equally among the processes if <code>n0</code> is divisible by the
110 <em>square</em> of the number of processes. In this case,
111 <code>local_ni</code> will equal <code>local_no</code>. Otherwise, they may be
112 different.
113 </p>
114 <p>For some applications, such as convolutions, the order of the output
115 data is irrelevant. In this case, performance can be improved by
116 specifying that the output data be stored in an FFTW-defined
117 &ldquo;scrambled&rdquo; format. (In particular, this is the analogue of
118 transposed output in the multidimensional case: scrambled output saves
119 a communications step.) If you pass <code>FFTW_MPI_SCRAMBLED_OUT</code> in
120 the flags, then the output is stored in this (undocumented) scrambled
121 order. Conversely, to perform the inverse transform of data in
122 scrambled order, pass the <code>FFTW_MPI_SCRAMBLED_IN</code> flag.
123 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT"></a>
124 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN"></a>
125 </p>
126
127 <p>In MPI FFTW, only composite sizes <code>n0</code> can be parallelized; we
128 have not yet implemented a parallel algorithm for large prime sizes.
129 </p>
130 <hr>
131 <div class="header">
132 <p>
133 Previous: <a href="Transposed-distributions.html#Transposed-distributions" accesskey="p" rel="prev">Transposed distributions</a>, Up: <a href="MPI-Data-Distribution.html#MPI-Data-Distribution" accesskey="u" rel="up">MPI Data Distribution</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>
134 </div>
135
136
137
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139 </html>