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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 d0c2a83c1364
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Chris@82 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
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Chris@82 6 Copyright (C) 2003 Matteo Frigo.
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Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: More DFTs of Real Data</title>
Chris@82 26
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Chris@82 36 <link href="Tutorial.html#Tutorial" rel="up" title="Tutorial">
Chris@82 37 <link href="The-Halfcomplex_002dformat-DFT.html#The-Halfcomplex_002dformat-DFT" rel="next" title="The Halfcomplex-format DFT">
Chris@82 38 <link href="Multi_002dDimensional-DFTs-of-Real-Data.html#Multi_002dDimensional-DFTs-of-Real-Data" rel="prev" title="Multi-Dimensional DFTs of Real Data">
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Chris@82 67
Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="More-DFTs-of-Real-Data"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Previous: <a href="Multi_002dDimensional-DFTs-of-Real-Data.html#Multi_002dDimensional-DFTs-of-Real-Data" accesskey="p" rel="prev">Multi-Dimensional DFTs of Real Data</a>, Up: <a href="Tutorial.html#Tutorial" accesskey="u" rel="up">Tutorial</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="More-DFTs-of-Real-Data-1"></a>
Chris@82 78 <h3 class="section">2.5 More DFTs of Real Data</h3>
Chris@82 79 <table class="menu" border="0" cellspacing="0">
Chris@82 80 <tr><td align="left" valign="top">&bull; <a href="The-Halfcomplex_002dformat-DFT.html#The-Halfcomplex_002dformat-DFT" accesskey="1">The Halfcomplex-format DFT</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 81 </td></tr>
Chris@82 82 <tr><td align="left" valign="top">&bull; <a href="Real-even_002fodd-DFTs-_0028cosine_002fsine-transforms_0029.html#Real-even_002fodd-DFTs-_0028cosine_002fsine-transforms_0029" accesskey="2">Real even/odd DFTs (cosine/sine transforms)</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 83 </td></tr>
Chris@82 84 <tr><td align="left" valign="top">&bull; <a href="The-Discrete-Hartley-Transform.html#The-Discrete-Hartley-Transform" accesskey="3">The Discrete Hartley Transform</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
Chris@82 85 </td></tr>
Chris@82 86 </table>
Chris@82 87
Chris@82 88 <p>FFTW supports several other transform types via a unified <em>r2r</em>
Chris@82 89 (real-to-real) interface,
Chris@82 90 <a name="index-r2r"></a>
Chris@82 91 so called because it takes a real (<code>double</code>) array and outputs a
Chris@82 92 real array of the same size. These r2r transforms currently fall into
Chris@82 93 three categories: DFTs of real input and complex-Hermitian output in
Chris@82 94 halfcomplex format, DFTs of real input with even/odd symmetry
Chris@82 95 (a.k.a. discrete cosine/sine transforms, DCTs/DSTs), and discrete
Chris@82 96 Hartley transforms (DHTs), all described in more detail by the
Chris@82 97 following sections.
Chris@82 98 </p>
Chris@82 99 <p>The r2r transforms follow the by now familiar interface of creating an
Chris@82 100 <code>fftw_plan</code>, executing it with <code>fftw_execute(plan)</code>, and
Chris@82 101 destroying it with <code>fftw_destroy_plan(plan)</code>. Furthermore, all
Chris@82 102 r2r transforms share the same planner interface:
Chris@82 103 </p>
Chris@82 104 <div class="example">
Chris@82 105 <pre class="example">fftw_plan fftw_plan_r2r_1d(int n, double *in, double *out,
Chris@82 106 fftw_r2r_kind kind, unsigned flags);
Chris@82 107 fftw_plan fftw_plan_r2r_2d(int n0, int n1, double *in, double *out,
Chris@82 108 fftw_r2r_kind kind0, fftw_r2r_kind kind1,
Chris@82 109 unsigned flags);
Chris@82 110 fftw_plan fftw_plan_r2r_3d(int n0, int n1, int n2,
Chris@82 111 double *in, double *out,
Chris@82 112 fftw_r2r_kind kind0,
Chris@82 113 fftw_r2r_kind kind1,
Chris@82 114 fftw_r2r_kind kind2,
Chris@82 115 unsigned flags);
Chris@82 116 fftw_plan fftw_plan_r2r(int rank, const int *n, double *in, double *out,
Chris@82 117 const fftw_r2r_kind *kind, unsigned flags);
Chris@82 118 </pre></div>
Chris@82 119 <a name="index-fftw_005fplan_005fr2r_005f1d"></a>
Chris@82 120 <a name="index-fftw_005fplan_005fr2r_005f2d"></a>
Chris@82 121 <a name="index-fftw_005fplan_005fr2r_005f3d"></a>
Chris@82 122 <a name="index-fftw_005fplan_005fr2r"></a>
Chris@82 123
Chris@82 124 <p>Just as for the complex DFT, these plan 1d/2d/3d/multi-dimensional
Chris@82 125 transforms for contiguous arrays in row-major order, transforming (real)
Chris@82 126 input to output of the same size, where <code>n</code> specifies the
Chris@82 127 <em>physical</em> dimensions of the arrays. All positive <code>n</code> are
Chris@82 128 supported (with the exception of <code>n=1</code> for the <code>FFTW_REDFT00</code>
Chris@82 129 kind, noted in the real-even subsection below); products of small
Chris@82 130 factors are most efficient (factorizing <code>n-1</code> and <code>n+1</code> for
Chris@82 131 <code>FFTW_REDFT00</code> and <code>FFTW_RODFT00</code> kinds, described below), but
Chris@82 132 an <i>O</i>(<i>n</i>&nbsp;log&nbsp;<i>n</i>)
Chris@82 133 algorithm is used even for prime sizes.
Chris@82 134 </p>
Chris@82 135 <p>Each dimension has a <em>kind</em> parameter, of type
Chris@82 136 <code>fftw_r2r_kind</code>, specifying the kind of r2r transform to be used
Chris@82 137 for that dimension.
Chris@82 138 <a name="index-kind-_0028r2r_0029"></a>
Chris@82 139 <a name="index-fftw_005fr2r_005fkind"></a>
Chris@82 140 (In the case of <code>fftw_plan_r2r</code>, this is an array <code>kind[rank]</code>
Chris@82 141 where <code>kind[i]</code> is the transform kind for the dimension
Chris@82 142 <code>n[i]</code>.) The kind can be one of a set of predefined constants,
Chris@82 143 defined in the following subsections.
Chris@82 144 </p>
Chris@82 145 <p>In other words, FFTW computes the separable product of the specified
Chris@82 146 r2r transforms over each dimension, which can be used e.g. for partial
Chris@82 147 differential equations with mixed boundary conditions. (For some r2r
Chris@82 148 kinds, notably the halfcomplex DFT and the DHT, such a separable
Chris@82 149 product is somewhat problematic in more than one dimension, however,
Chris@82 150 as is described below.)
Chris@82 151 </p>
Chris@82 152 <p>In the current version of FFTW, all r2r transforms except for the
Chris@82 153 halfcomplex type are computed via pre- or post-processing of
Chris@82 154 halfcomplex transforms, and they are therefore not as fast as they
Chris@82 155 could be. Since most other general DCT/DST codes employ a similar
Chris@82 156 algorithm, however, FFTW&rsquo;s implementation should provide at least
Chris@82 157 competitive performance.
Chris@82 158 </p>
Chris@82 159 <hr>
Chris@82 160 <div class="header">
Chris@82 161 <p>
Chris@82 162 Previous: <a href="Multi_002dDimensional-DFTs-of-Real-Data.html#Multi_002dDimensional-DFTs-of-Real-Data" accesskey="p" rel="prev">Multi-Dimensional DFTs of Real Data</a>, Up: <a href="Tutorial.html#Tutorial" accesskey="u" rel="up">Tutorial</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@82 163 </div>
Chris@82 164
Chris@82 165
Chris@82 166
Chris@82 167 </body>
Chris@82 168 </html>