Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.8/doc/html/Guru-vector-and-transform-sizes.html @ 82:d0c2a83c1364

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
parents
children
rev   line source
Chris@82 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Chris@82 2 <html>
Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
Chris@82 5
Chris@82 6 Copyright (C) 2003 Matteo Frigo.
Chris@82 7
Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
Chris@82 9
Chris@82 10 Permission is granted to make and distribute verbatim copies of this
Chris@82 11 manual provided the copyright notice and this permission notice are
Chris@82 12 preserved on all copies.
Chris@82 13
Chris@82 14 Permission is granted to copy and distribute modified versions of this
Chris@82 15 manual under the conditions for verbatim copying, provided that the
Chris@82 16 entire resulting derived work is distributed under the terms of a
Chris@82 17 permission notice identical to this one.
Chris@82 18
Chris@82 19 Permission is granted to copy and distribute translations of this manual
Chris@82 20 into another language, under the above conditions for modified versions,
Chris@82 21 except that this permission notice may be stated in a translation
Chris@82 22 approved by the Free Software Foundation. -->
Chris@82 23 <!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: Guru vector and transform sizes</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: Guru vector and transform sizes">
Chris@82 28 <meta name="keywords" content="FFTW 3.3.8: Guru vector and transform sizes">
Chris@82 29 <meta name="resource-type" content="document">
Chris@82 30 <meta name="distribution" content="global">
Chris@82 31 <meta name="Generator" content="makeinfo">
Chris@82 32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Chris@82 33 <link href="index.html#Top" rel="start" title="Top">
Chris@82 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
Chris@82 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@82 36 <link href="Guru-Interface.html#Guru-Interface" rel="up" title="Guru Interface">
Chris@82 37 <link href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" rel="next" title="Guru Complex DFTs">
Chris@82 38 <link href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays" rel="prev" title="Interleaved and split arrays">
Chris@82 39 <style type="text/css">
Chris@82 40 <!--
Chris@82 41 a.summary-letter {text-decoration: none}
Chris@82 42 blockquote.indentedblock {margin-right: 0em}
Chris@82 43 blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
Chris@82 44 blockquote.smallquotation {font-size: smaller}
Chris@82 45 div.display {margin-left: 3.2em}
Chris@82 46 div.example {margin-left: 3.2em}
Chris@82 47 div.lisp {margin-left: 3.2em}
Chris@82 48 div.smalldisplay {margin-left: 3.2em}
Chris@82 49 div.smallexample {margin-left: 3.2em}
Chris@82 50 div.smalllisp {margin-left: 3.2em}
Chris@82 51 kbd {font-style: oblique}
Chris@82 52 pre.display {font-family: inherit}
Chris@82 53 pre.format {font-family: inherit}
Chris@82 54 pre.menu-comment {font-family: serif}
Chris@82 55 pre.menu-preformatted {font-family: serif}
Chris@82 56 pre.smalldisplay {font-family: inherit; font-size: smaller}
Chris@82 57 pre.smallexample {font-size: smaller}
Chris@82 58 pre.smallformat {font-family: inherit; font-size: smaller}
Chris@82 59 pre.smalllisp {font-size: smaller}
Chris@82 60 span.nolinebreak {white-space: nowrap}
Chris@82 61 span.roman {font-family: initial; font-weight: normal}
Chris@82 62 span.sansserif {font-family: sans-serif; font-weight: normal}
Chris@82 63 ul.no-bullet {list-style: none}
Chris@82 64 -->
Chris@82 65 </style>
Chris@82 66
Chris@82 67
Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Guru-vector-and-transform-sizes"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" accesskey="n" rel="next">Guru Complex DFTs</a>, Previous: <a href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays" accesskey="p" rel="prev">Interleaved and split arrays</a>, Up: <a href="Guru-Interface.html#Guru-Interface" accesskey="u" rel="up">Guru Interface</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@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="Guru-vector-and-transform-sizes-1"></a>
Chris@82 78 <h4 class="subsection">4.5.2 Guru vector and transform sizes</h4>
Chris@82 79
Chris@82 80 <p>The guru interface introduces one basic new data structure,
Chris@82 81 <code>fftw_iodim</code>, that is used to specify sizes and strides for
Chris@82 82 multi-dimensional transforms and vectors:
Chris@82 83 </p>
Chris@82 84 <div class="example">
Chris@82 85 <pre class="example">typedef struct {
Chris@82 86 int n;
Chris@82 87 int is;
Chris@82 88 int os;
Chris@82 89 } fftw_iodim;
Chris@82 90 </pre></div>
Chris@82 91 <a name="index-fftw_005fiodim"></a>
Chris@82 92
Chris@82 93 <p>Here, <code>n</code> is the size of the dimension, and <code>is</code> and <code>os</code>
Chris@82 94 are the strides of that dimension for the input and output arrays. (The
Chris@82 95 stride is the separation of consecutive elements along this dimension.)
Chris@82 96 </p>
Chris@82 97 <p>The meaning of the stride parameter depends on the type of the array
Chris@82 98 that the stride refers to. <em>If the array is interleaved complex,
Chris@82 99 strides are expressed in units of complex numbers
Chris@82 100 (<code>fftw_complex</code>). If the array is split complex or real, strides
Chris@82 101 are expressed in units of real numbers (<code>double</code>).</em> This
Chris@82 102 convention is consistent with the usual pointer arithmetic in the C
Chris@82 103 language. An interleaved array is denoted by a pointer <code>p</code> to
Chris@82 104 <code>fftw_complex</code>, so that <code>p+1</code> points to the next complex
Chris@82 105 number. Split arrays are denoted by pointers to <code>double</code>, in
Chris@82 106 which case pointer arithmetic operates in units of
Chris@82 107 <code>sizeof(double)</code>.
Chris@82 108 <a name="index-stride-2"></a>
Chris@82 109 </p>
Chris@82 110
Chris@82 111 <p>The guru planner interfaces all take a (<code>rank</code>, <code>dims[rank]</code>)
Chris@82 112 pair describing the transform size, and a (<code>howmany_rank</code>,
Chris@82 113 <code>howmany_dims[howmany_rank]</code>) pair describing the &ldquo;vector&rdquo; size (a
Chris@82 114 multi-dimensional loop of transforms to perform), where <code>dims</code> and
Chris@82 115 <code>howmany_dims</code> are arrays of <code>fftw_iodim</code>. Each <code>n</code> field must
Chris@82 116 be positive for <code>dims</code> and nonnegative for <code>howmany_dims</code>, while both
Chris@82 117 <code>rank</code> and <code>howmany_rank</code> must be nonnegative.
Chris@82 118 </p>
Chris@82 119 <p>For example, the <code>howmany</code> parameter in the advanced complex-DFT
Chris@82 120 interface corresponds to <code>howmany_rank</code> = 1,
Chris@82 121 <code>howmany_dims[0].n</code> = <code>howmany</code>, <code>howmany_dims[0].is</code> =
Chris@82 122 <code>idist</code>, and <code>howmany_dims[0].os</code> = <code>odist</code>.
Chris@82 123 <a name="index-howmany-loop"></a>
Chris@82 124 <a name="index-dist-1"></a>
Chris@82 125 (To compute a single transform, you can just use <code>howmany_rank</code> = 0.)
Chris@82 126 </p>
Chris@82 127
Chris@82 128 <p>A row-major multidimensional array with dimensions <code>n[rank]</code>
Chris@82 129 (see <a href="Row_002dmajor-Format.html#Row_002dmajor-Format">Row-major Format</a>) corresponds to <code>dims[i].n</code> =
Chris@82 130 <code>n[i]</code> and the recurrence <code>dims[i].is</code> = <code>n[i+1] *
Chris@82 131 dims[i+1].is</code> (similarly for <code>os</code>). The stride of the last
Chris@82 132 (<code>i=rank-1</code>) dimension is the overall stride of the array.
Chris@82 133 e.g. to be equivalent to the advanced complex-DFT interface, you would
Chris@82 134 have <code>dims[rank-1].is</code> = <code>istride</code> and
Chris@82 135 <code>dims[rank-1].os</code> = <code>ostride</code>.
Chris@82 136 <a name="index-row_002dmajor-3"></a>
Chris@82 137 </p>
Chris@82 138
Chris@82 139 <p>In general, we only guarantee FFTW to return a non-<code>NULL</code> plan if
Chris@82 140 the vector and transform dimensions correspond to a set of distinct
Chris@82 141 indices, and for in-place transforms the input/output strides should
Chris@82 142 be the same.
Chris@82 143 </p>
Chris@82 144 <hr>
Chris@82 145 <div class="header">
Chris@82 146 <p>
Chris@82 147 Next: <a href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" accesskey="n" rel="next">Guru Complex DFTs</a>, Previous: <a href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays" accesskey="p" rel="prev">Interleaved and split arrays</a>, Up: <a href="Guru-Interface.html#Guru-Interface" accesskey="u" rel="up">Guru Interface</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@82 148 </div>
Chris@82 149
Chris@82 150
Chris@82 151
Chris@82 152 </body>
Chris@82 153 </html>