Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.5/doc/html/One_002ddimensional-distributions.html @ 127:7867fa7e1b6b

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
parents
children
rev   line source
cannam@127 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
cannam@127 2 <html>
cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
cannam@127 7
cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
cannam@127 9
cannam@127 10 Permission is granted to make and distribute verbatim copies of this
cannam@127 11 manual provided the copyright notice and this permission notice are
cannam@127 12 preserved on all copies.
cannam@127 13
cannam@127 14 Permission is granted to copy and distribute modified versions of this
cannam@127 15 manual under the conditions for verbatim copying, provided that the
cannam@127 16 entire resulting derived work is distributed under the terms of a
cannam@127 17 permission notice identical to this one.
cannam@127 18
cannam@127 19 Permission is granted to copy and distribute translations of this manual
cannam@127 20 into another language, under the above conditions for modified versions,
cannam@127 21 except that this permission notice may be stated in a translation
cannam@127 22 approved by the Free Software Foundation. -->
cannam@127 23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: One-dimensional distributions</title>
cannam@127 26
cannam@127 27 <meta name="description" content="FFTW 3.3.5: One-dimensional distributions">
cannam@127 28 <meta name="keywords" content="FFTW 3.3.5: One-dimensional distributions">
cannam@127 29 <meta name="resource-type" content="document">
cannam@127 30 <meta name="distribution" content="global">
cannam@127 31 <meta name="Generator" content="makeinfo">
cannam@127 32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
cannam@127 33 <link href="index.html#Top" rel="start" title="Top">
cannam@127 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
cannam@127 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
cannam@127 36 <link href="MPI-Data-Distribution.html#MPI-Data-Distribution" rel="up" title="MPI Data Distribution">
cannam@127 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@127 38 <link href="Transposed-distributions.html#Transposed-distributions" rel="prev" title="Transposed distributions">
cannam@127 39 <style type="text/css">
cannam@127 40 <!--
cannam@127 41 a.summary-letter {text-decoration: none}
cannam@127 42 blockquote.smallquotation {font-size: smaller}
cannam@127 43 div.display {margin-left: 3.2em}
cannam@127 44 div.example {margin-left: 3.2em}
cannam@127 45 div.indentedblock {margin-left: 3.2em}
cannam@127 46 div.lisp {margin-left: 3.2em}
cannam@127 47 div.smalldisplay {margin-left: 3.2em}
cannam@127 48 div.smallexample {margin-left: 3.2em}
cannam@127 49 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
cannam@127 50 div.smalllisp {margin-left: 3.2em}
cannam@127 51 kbd {font-style:oblique}
cannam@127 52 pre.display {font-family: inherit}
cannam@127 53 pre.format {font-family: inherit}
cannam@127 54 pre.menu-comment {font-family: serif}
cannam@127 55 pre.menu-preformatted {font-family: serif}
cannam@127 56 pre.smalldisplay {font-family: inherit; font-size: smaller}
cannam@127 57 pre.smallexample {font-size: smaller}
cannam@127 58 pre.smallformat {font-family: inherit; font-size: smaller}
cannam@127 59 pre.smalllisp {font-size: smaller}
cannam@127 60 span.nocodebreak {white-space:nowrap}
cannam@127 61 span.nolinebreak {white-space:nowrap}
cannam@127 62 span.roman {font-family:serif; font-weight:normal}
cannam@127 63 span.sansserif {font-family:sans-serif; font-weight:normal}
cannam@127 64 ul.no-bullet {list-style: none}
cannam@127 65 -->
cannam@127 66 </style>
cannam@127 67
cannam@127 68
cannam@127 69 </head>
cannam@127 70
cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="One_002ddimensional-distributions"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="One_002ddimensional-distributions-1"></a>
cannam@127 79 <h4 class="subsection">6.4.4 One-dimensional distributions</h4>
cannam@127 80
cannam@127 81 <p>For one-dimensional distributed DFTs using FFTW, matters are slightly
cannam@127 82 more complicated because the data distribution is more closely tied to
cannam@127 83 how the algorithm works. In particular, you can no longer pass an
cannam@127 84 arbitrary block size and must accept FFTW&rsquo;s default; also, the block
cannam@127 85 sizes may be different for input and output. Also, the data
cannam@127 86 distribution depends on the flags and transform direction, in order
cannam@127 87 for forward and backward transforms to work correctly.
cannam@127 88 </p>
cannam@127 89 <div class="example">
cannam@127 90 <pre class="example">ptrdiff_t fftw_mpi_local_size_1d(ptrdiff_t n0, MPI_Comm comm,
cannam@127 91 int sign, unsigned flags,
cannam@127 92 ptrdiff_t *local_ni, ptrdiff_t *local_i_start,
cannam@127 93 ptrdiff_t *local_no, ptrdiff_t *local_o_start);
cannam@127 94 </pre></div>
cannam@127 95 <a name="index-fftw_005fmpi_005flocal_005fsize_005f1d"></a>
cannam@127 96
cannam@127 97 <p>This function computes the data distribution for a 1d transform of
cannam@127 98 size <code>n0</code> with the given transform <code>sign</code> and <code>flags</code>.
cannam@127 99 Both input and output data use block distributions. The input on the
cannam@127 100 current process will consist of <code>local_ni</code> numbers starting at
cannam@127 101 index <code>local_i_start</code>; e.g. if only a single process is used,
cannam@127 102 then <code>local_ni</code> will be <code>n0</code> and <code>local_i_start</code> will
cannam@127 103 be <code>0</code>. Similarly for the output, with <code>local_no</code> numbers
cannam@127 104 starting at index <code>local_o_start</code>. The return value of
cannam@127 105 <code>fftw_mpi_local_size_1d</code> will be the total number of elements to
cannam@127 106 allocate on the current process (which might be slightly larger than
cannam@127 107 the local size due to intermediate steps in the algorithm).
cannam@127 108 </p>
cannam@127 109 <p>As mentioned above (see <a href="Load-balancing.html#Load-balancing">Load balancing</a>), the data will be divided
cannam@127 110 equally among the processes if <code>n0</code> is divisible by the
cannam@127 111 <em>square</em> of the number of processes. In this case,
cannam@127 112 <code>local_ni</code> will equal <code>local_no</code>. Otherwise, they may be
cannam@127 113 different.
cannam@127 114 </p>
cannam@127 115 <p>For some applications, such as convolutions, the order of the output
cannam@127 116 data is irrelevant. In this case, performance can be improved by
cannam@127 117 specifying that the output data be stored in an FFTW-defined
cannam@127 118 &ldquo;scrambled&rdquo; format. (In particular, this is the analogue of
cannam@127 119 transposed output in the multidimensional case: scrambled output saves
cannam@127 120 a communications step.) If you pass <code>FFTW_MPI_SCRAMBLED_OUT</code> in
cannam@127 121 the flags, then the output is stored in this (undocumented) scrambled
cannam@127 122 order. Conversely, to perform the inverse transform of data in
cannam@127 123 scrambled order, pass the <code>FFTW_MPI_SCRAMBLED_IN</code> flag.
cannam@127 124 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fOUT"></a>
cannam@127 125 <a name="index-FFTW_005fMPI_005fSCRAMBLED_005fIN"></a>
cannam@127 126 </p>
cannam@127 127
cannam@127 128 <p>In MPI FFTW, only composite sizes <code>n0</code> can be parallelized; we
cannam@127 129 have not yet implemented a parallel algorithm for large prime sizes.
cannam@127 130 </p>
cannam@127 131 <hr>
cannam@127 132 <div class="header">
cannam@127 133 <p>
cannam@127 134 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>
cannam@127 135 </div>
cannam@127 136
cannam@127 137
cannam@127 138
cannam@127 139 </body>
cannam@127 140 </html>