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Replace these with versions built using an older toolset (so as to avoid ABI compatibilities when linking on Ubuntu 14.04 for packaging purposes)
author Chris Cannam
date Fri, 07 Feb 2020 11:51:13 +0000
parents 2cd0e3b3e1fd
children
rev   line source
Chris@42 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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Chris@42 3 <!-- This manual is for FFTW
Chris@42 4 (version 3.3.5, 30 July 2016).
Chris@42 5
Chris@42 6 Copyright (C) 2003 Matteo Frigo.
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Chris@42 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: One-dimensional distributions</title>
Chris@42 26
Chris@42 27 <meta name="description" content="FFTW 3.3.5: One-dimensional distributions">
Chris@42 28 <meta name="keywords" content="FFTW 3.3.5: One-dimensional distributions">
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Chris@42 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@42 36 <link href="MPI-Data-Distribution.html#MPI-Data-Distribution" rel="up" title="MPI Data Distribution">
Chris@42 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">
Chris@42 38 <link href="Transposed-distributions.html#Transposed-distributions" rel="prev" title="Transposed distributions">
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Chris@42 67
Chris@42 68
Chris@42 69 </head>
Chris@42 70
Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="One_002ddimensional-distributions"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 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>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="One_002ddimensional-distributions-1"></a>
Chris@42 79 <h4 class="subsection">6.4.4 One-dimensional distributions</h4>
Chris@42 80
Chris@42 81 <p>For one-dimensional distributed DFTs using FFTW, matters are slightly
Chris@42 82 more complicated because the data distribution is more closely tied to
Chris@42 83 how the algorithm works. In particular, you can no longer pass an
Chris@42 84 arbitrary block size and must accept FFTW&rsquo;s default; also, the block
Chris@42 85 sizes may be different for input and output. Also, the data
Chris@42 86 distribution depends on the flags and transform direction, in order
Chris@42 87 for forward and backward transforms to work correctly.
Chris@42 88 </p>
Chris@42 89 <div class="example">
Chris@42 90 <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(ptrdiff_t n0, MPI_Comm comm,
Chris@42 91 int sign, unsigned flags,
Chris@42 92 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
Chris@42 93 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
Chris@42 94 </pre></div>
Chris@42 95 <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d"></a>
Chris@42 96
Chris@42 97 <p>This function computes the data distribution for a 1d transform of
Chris@42 98 size <code>n0</code> with the given transform <code>sign</code> and <code>flags</code>.
Chris@42 99 Both input and output data use block distributions. The input on the
Chris@42 100 current process will consist of <code>local_ni</code> numbers starting at
Chris@42 101 index <code>local_i_start</code>; e.g. if only a single process is used,
Chris@42 102 then <code>local_ni</code> will be <code>n0</code> and <code>local_i_start</code> will
Chris@42 103 be <code>0</code>. Similarly for the output, with <code>local_no</code> numbers
Chris@42 104 starting at index <code>local_o_start</code>. The return value of
Chris@42 105 <code>fftw_mpi_local_size_1d</code> will be the total number of elements to
Chris@42 106 allocate on the current process (which might be slightly larger than
Chris@42 107 the local size due to intermediate steps in the algorithm).
Chris@42 108 </p>
Chris@42 109 <p>As mentioned above (see <a href="Load-balancing.html#Load-balancing">Load balancing</a>), the data will be divided
Chris@42 110 equally among the processes if <code>n0</code> is divisible by the
Chris@42 111 <em>square</em> of the number of processes. In this case,
Chris@42 112 <code>local_ni</code> will equal <code>local_no</code>. Otherwise, they may be
Chris@42 113 different.
Chris@42 114 </p>
Chris@42 115 <p>For some applications, such as convolutions, the order of the output
Chris@42 116 data is irrelevant. In this case, performance can be improved by
Chris@42 117 specifying that the output data be stored in an FFTW-defined
Chris@42 118 &ldquo;scrambled&rdquo; format. (In particular, this is the analogue of
Chris@42 119 transposed output in the multidimensional case: scrambled output saves
Chris@42 120 a communications step.) If you pass <code>FFTW_MPI_SCRAMBLED_OUT</code> in
Chris@42 121 the flags, then the output is stored in this (undocumented) scrambled
Chris@42 122 order. Conversely, to perform the inverse transform of data in
Chris@42 123 scrambled order, pass the <code>FFTW_MPI_SCRAMBLED_IN</code> flag.
Chris@42 124 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT"></a>
Chris@42 125 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN"></a>
Chris@42 126 </p>
Chris@42 127
Chris@42 128 <p>In MPI FFTW, only composite sizes <code>n0</code> can be parallelized; we
Chris@42 129 have not yet implemented a parallel algorithm for large prime sizes.
Chris@42 130 </p>
Chris@42 131 <hr>
Chris@42 132 <div class="header">
Chris@42 133 <p>
Chris@42 134 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>
Chris@42 135 </div>
Chris@42 136
Chris@42 137
Chris@42 138
Chris@42 139 </body>
Chris@42 140 </html>