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Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
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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).
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Chris@42 6 Copyright (C) 2003 Matteo Frigo.
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Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Guru Complex DFTs</title>
Chris@42 26
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Chris@42 37 <link href="Guru-Real_002ddata-DFTs.html#Guru-Real_002ddata-DFTs" rel="next" title="Guru Real-data DFTs">
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Chris@42 70
Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="Guru-Complex-DFTs"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 Next: <a href="Guru-Real_002ddata-DFTs.html#Guru-Real_002ddata-DFTs" accesskey="n" rel="next">Guru Real-data DFTs</a>, Previous: <a href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes" accesskey="p" rel="prev">Guru vector and transform sizes</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@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Guru-Complex-DFTs-1"></a>
Chris@42 79 <h4 class="subsection">4.5.3 Guru Complex DFTs</h4>
Chris@42 80
Chris@42 81 <div class="example">
Chris@42 82 <pre class="example">fftw_plan fftw_plan_guru_dft(
Chris@42 83 int rank, const fftw_iodim *dims,
Chris@42 84 int howmany_rank, const fftw_iodim *howmany_dims,
Chris@42 85 fftw_complex *in, fftw_complex *out,
Chris@42 86 int sign, unsigned flags);
Chris@42 87
Chris@42 88 fftw_plan fftw_plan_guru_split_dft(
Chris@42 89 int rank, const fftw_iodim *dims,
Chris@42 90 int howmany_rank, const fftw_iodim *howmany_dims,
Chris@42 91 double *ri, double *ii, double *ro, double *io,
Chris@42 92 unsigned flags);
Chris@42 93 </pre></div>
Chris@42 94 <a name="index-fftw_005fplan_005fguru_005fdft"></a>
Chris@42 95 <a name="index-fftw_005fplan_005fguru_005fsplit_005fdft"></a>
Chris@42 96
Chris@42 97 <p>These two functions plan a complex-data, multi-dimensional DFT
Chris@42 98 for the interleaved and split format, respectively.
Chris@42 99 Transform dimensions are given by (<code>rank</code>, <code>dims</code>) over a
Chris@42 100 multi-dimensional vector (loop) of dimensions (<code>howmany_rank</code>,
Chris@42 101 <code>howmany_dims</code>). <code>dims</code> and <code>howmany_dims</code> should point
Chris@42 102 to <code>fftw_iodim</code> arrays of length <code>rank</code> and
Chris@42 103 <code>howmany_rank</code>, respectively.
Chris@42 104 </p>
Chris@42 105 <a name="index-flags-5"></a>
Chris@42 106 <p><code>flags</code> is a bitwise OR (&lsquo;<samp>|</samp>&rsquo;) of zero or more planner flags,
Chris@42 107 as defined in <a href="Planner-Flags.html#Planner-Flags">Planner Flags</a>.
Chris@42 108 </p>
Chris@42 109 <p>In the <code>fftw_plan_guru_dft</code> function, the pointers <code>in</code> and
Chris@42 110 <code>out</code> point to the interleaved input and output arrays,
Chris@42 111 respectively. The sign can be either <em>-1</em> (=
Chris@42 112 <code>FFTW_FORWARD</code>) or <em>+1</em> (= <code>FFTW_BACKWARD</code>). If the
Chris@42 113 pointers are equal, the transform is in-place.
Chris@42 114 </p>
Chris@42 115 <p>In the <code>fftw_plan_guru_split_dft</code> function,
Chris@42 116 <code>ri</code> and <code>ii</code> point to the real and imaginary input arrays,
Chris@42 117 and <code>ro</code> and <code>io</code> point to the real and imaginary output
Chris@42 118 arrays. The input and output pointers may be the same, indicating an
Chris@42 119 in-place transform. For example, for <code>fftw_complex</code> pointers
Chris@42 120 <code>in</code> and <code>out</code>, the corresponding parameters are:
Chris@42 121 </p>
Chris@42 122 <div class="example">
Chris@42 123 <pre class="example">ri = (double *) in;
Chris@42 124 ii = (double *) in + 1;
Chris@42 125 ro = (double *) out;
Chris@42 126 io = (double *) out + 1;
Chris@42 127 </pre></div>
Chris@42 128
Chris@42 129 <p>Because <code>fftw_plan_guru_split_dft</code> accepts split arrays, strides
Chris@42 130 are expressed in units of <code>double</code>. For a contiguous
Chris@42 131 <code>fftw_complex</code> array, the overall stride of the transform should
Chris@42 132 be 2, the distance between consecutive real parts or between
Chris@42 133 consecutive imaginary parts; see <a href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes">Guru vector and transform sizes</a>. Note that the dimension strides are applied equally to the
Chris@42 134 real and imaginary parts; real and imaginary arrays with different
Chris@42 135 strides are not supported.
Chris@42 136 </p>
Chris@42 137 <p>There is no <code>sign</code> parameter in <code>fftw_plan_guru_split_dft</code>.
Chris@42 138 This function always plans for an <code>FFTW_FORWARD</code> transform. To
Chris@42 139 plan for an <code>FFTW_BACKWARD</code> transform, you can exploit the
Chris@42 140 identity that the backwards DFT is equal to the forwards DFT with the
Chris@42 141 real and imaginary parts swapped. For example, in the case of the
Chris@42 142 <code>fftw_complex</code> arrays above, the <code>FFTW_BACKWARD</code> transform
Chris@42 143 is computed by the parameters:
Chris@42 144 </p>
Chris@42 145 <div class="example">
Chris@42 146 <pre class="example">ri = (double *) in + 1;
Chris@42 147 ii = (double *) in;
Chris@42 148 ro = (double *) out + 1;
Chris@42 149 io = (double *) out;
Chris@42 150 </pre></div>
Chris@42 151
Chris@42 152 <hr>
Chris@42 153 <div class="header">
Chris@42 154 <p>
Chris@42 155 Next: <a href="Guru-Real_002ddata-DFTs.html#Guru-Real_002ddata-DFTs" accesskey="n" rel="next">Guru Real-data DFTs</a>, Previous: <a href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes" accesskey="p" rel="prev">Guru vector and transform sizes</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@42 156 </div>
Chris@42 157
Chris@42 158
Chris@42 159
Chris@42 160 </body>
Chris@42 161 </html>