Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.8/doc/html/One_002ddimensional-distributions.html @ 169:223a55898ab9 tip default

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Add null config files
author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
parents bd3cc4d1df30
children
rev   line source
cannam@167 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
cannam@167 2 <html>
cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
cannam@167 7
cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
cannam@167 9
cannam@167 10 Permission is granted to make and distribute verbatim copies of this
cannam@167 11 manual provided the copyright notice and this permission notice are
cannam@167 12 preserved on all copies.
cannam@167 13
cannam@167 14 Permission is granted to copy and distribute modified versions of this
cannam@167 15 manual under the conditions for verbatim copying, provided that the
cannam@167 16 entire resulting derived work is distributed under the terms of a
cannam@167 17 permission notice identical to this one.
cannam@167 18
cannam@167 19 Permission is granted to copy and distribute translations of this manual
cannam@167 20 into another language, under the above conditions for modified versions,
cannam@167 21 except that this permission notice may be stated in a translation
cannam@167 22 approved by the Free Software Foundation. -->
cannam@167 23 <!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: One-dimensional distributions</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: One-dimensional distributions">
cannam@167 28 <meta name="keywords" content="FFTW 3.3.8: One-dimensional distributions">
cannam@167 29 <meta name="resource-type" content="document">
cannam@167 30 <meta name="distribution" content="global">
cannam@167 31 <meta name="Generator" content="makeinfo">
cannam@167 32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
cannam@167 33 <link href="index.html#Top" rel="start" title="Top">
cannam@167 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
cannam@167 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
cannam@167 36 <link href="MPI-Data-Distribution.html#MPI-Data-Distribution" rel="up" title="MPI Data Distribution">
cannam@167 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">
cannam@167 38 <link href="Transposed-distributions.html#Transposed-distributions" rel="prev" title="Transposed distributions">
cannam@167 39 <style type="text/css">
cannam@167 40 <!--
cannam@167 41 a.summary-letter {text-decoration: none}
cannam@167 42 blockquote.indentedblock {margin-right: 0em}
cannam@167 43 blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
cannam@167 44 blockquote.smallquotation {font-size: smaller}
cannam@167 45 div.display {margin-left: 3.2em}
cannam@167 46 div.example {margin-left: 3.2em}
cannam@167 47 div.lisp {margin-left: 3.2em}
cannam@167 48 div.smalldisplay {margin-left: 3.2em}
cannam@167 49 div.smallexample {margin-left: 3.2em}
cannam@167 50 div.smalllisp {margin-left: 3.2em}
cannam@167 51 kbd {font-style: oblique}
cannam@167 52 pre.display {font-family: inherit}
cannam@167 53 pre.format {font-family: inherit}
cannam@167 54 pre.menu-comment {font-family: serif}
cannam@167 55 pre.menu-preformatted {font-family: serif}
cannam@167 56 pre.smalldisplay {font-family: inherit; font-size: smaller}
cannam@167 57 pre.smallexample {font-size: smaller}
cannam@167 58 pre.smallformat {font-family: inherit; font-size: smaller}
cannam@167 59 pre.smalllisp {font-size: smaller}
cannam@167 60 span.nolinebreak {white-space: nowrap}
cannam@167 61 span.roman {font-family: initial; font-weight: normal}
cannam@167 62 span.sansserif {font-family: sans-serif; font-weight: normal}
cannam@167 63 ul.no-bullet {list-style: none}
cannam@167 64 -->
cannam@167 65 </style>
cannam@167 66
cannam@167 67
cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="One_002ddimensional-distributions"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="One_002ddimensional-distributions-1"></a>
cannam@167 78 <h4 class="subsection">6.4.4 One-dimensional distributions</h4>
cannam@167 79
cannam@167 80 <p>For one-dimensional distributed DFTs using FFTW, matters are slightly
cannam@167 81 more complicated because the data distribution is more closely tied to
cannam@167 82 how the algorithm works. In particular, you can no longer pass an
cannam@167 83 arbitrary block size and must accept FFTW&rsquo;s default; also, the block
cannam@167 84 sizes may be different for input and output. Also, the data
cannam@167 85 distribution depends on the flags and transform direction, in order
cannam@167 86 for forward and backward transforms to work correctly.
cannam@167 87 </p>
cannam@167 88 <div class="example">
cannam@167 89 <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(ptrdiff_t n0, MPI_Comm comm,
cannam@167 90 int sign, unsigned flags,
cannam@167 91 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
cannam@167 92 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
cannam@167 93 </pre></div>
cannam@167 94 <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d"></a>
cannam@167 95
cannam@167 96 <p>This function computes the data distribution for a 1d transform of
cannam@167 97 size <code>n0</code> with the given transform <code>sign</code> and <code>flags</code>.
cannam@167 98 Both input and output data use block distributions. The input on the
cannam@167 99 current process will consist of <code>local_ni</code> numbers starting at
cannam@167 100 index <code>local_i_start</code>; e.g. if only a single process is used,
cannam@167 101 then <code>local_ni</code> will be <code>n0</code> and <code>local_i_start</code> will
cannam@167 102 be <code>0</code>. Similarly for the output, with <code>local_no</code> numbers
cannam@167 103 starting at index <code>local_o_start</code>. The return value of
cannam@167 104 <code>fftw_mpi_local_size_1d</code> will be the total number of elements to
cannam@167 105 allocate on the current process (which might be slightly larger than
cannam@167 106 the local size due to intermediate steps in the algorithm).
cannam@167 107 </p>
cannam@167 108 <p>As mentioned above (see <a href="Load-balancing.html#Load-balancing">Load balancing</a>), the data will be divided
cannam@167 109 equally among the processes if <code>n0</code> is divisible by the
cannam@167 110 <em>square</em> of the number of processes. In this case,
cannam@167 111 <code>local_ni</code> will equal <code>local_no</code>. Otherwise, they may be
cannam@167 112 different.
cannam@167 113 </p>
cannam@167 114 <p>For some applications, such as convolutions, the order of the output
cannam@167 115 data is irrelevant. In this case, performance can be improved by
cannam@167 116 specifying that the output data be stored in an FFTW-defined
cannam@167 117 &ldquo;scrambled&rdquo; format. (In particular, this is the analogue of
cannam@167 118 transposed output in the multidimensional case: scrambled output saves
cannam@167 119 a communications step.) If you pass <code>FFTW_MPI_SCRAMBLED_OUT</code> in
cannam@167 120 the flags, then the output is stored in this (undocumented) scrambled
cannam@167 121 order. Conversely, to perform the inverse transform of data in
cannam@167 122 scrambled order, pass the <code>FFTW_MPI_SCRAMBLED_IN</code> flag.
cannam@167 123 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT"></a>
cannam@167 124 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN"></a>
cannam@167 125 </p>
cannam@167 126
cannam@167 127 <p>In MPI FFTW, only composite sizes <code>n0</code> can be parallelized; we
cannam@167 128 have not yet implemented a parallel algorithm for large prime sizes.
cannam@167 129 </p>
cannam@167 130 <hr>
cannam@167 131 <div class="header">
cannam@167 132 <p>
cannam@167 133 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>
cannam@167 134 </div>
cannam@167 135
cannam@167 136
cannam@167 137
cannam@167 138 </body>
cannam@167 139 </html>