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Current fftw source
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 18 Oct 2016 13:40:26 +0100
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3 <!-- This manual is for FFTW
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6 Copyright (C) 2003 Matteo Frigo.
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25 <title>FFTW 3.3.5: Guru Real-data DFTs</title>
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72 <a name="Guru-Real_002ddata-DFTs"></a>
73 <div class="header">
74 <p>
75 Next: <a href="Guru-Real_002dto_002dreal-Transforms.html#Guru-Real_002dto_002dreal-Transforms" accesskey="n" rel="next">Guru Real-to-real Transforms</a>, Previous: <a href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" accesskey="p" rel="prev">Guru Complex DFTs</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>
76 </div>
77 <hr>
78 <a name="Guru-Real_002ddata-DFTs-1"></a>
79 <h4 class="subsection">4.5.4 Guru Real-data DFTs</h4>
80
81 <div class="example">
82 <pre class="example">fftw_plan fftw_plan_guru_dft_r2c(
83 int rank, const fftw_iodim *dims,
84 int howmany_rank, const fftw_iodim *howmany_dims,
85 double *in, fftw_complex *out,
86 unsigned flags);
87
88 fftw_plan fftw_plan_guru_split_dft_r2c(
89 int rank, const fftw_iodim *dims,
90 int howmany_rank, const fftw_iodim *howmany_dims,
91 double *in, double *ro, double *io,
92 unsigned flags);
93
94 fftw_plan fftw_plan_guru_dft_c2r(
95 int rank, const fftw_iodim *dims,
96 int howmany_rank, const fftw_iodim *howmany_dims,
97 fftw_complex *in, double *out,
98 unsigned flags);
99
100 fftw_plan fftw_plan_guru_split_dft_c2r(
101 int rank, const fftw_iodim *dims,
102 int howmany_rank, const fftw_iodim *howmany_dims,
103 double *ri, double *ii, double *out,
104 unsigned flags);
105 </pre></div>
106 <a name="index-fftw_005fplan_005fguru_005fdft_005fr2c"></a>
107 <a name="index-fftw_005fplan_005fguru_005fsplit_005fdft_005fr2c"></a>
108 <a name="index-fftw_005fplan_005fguru_005fdft_005fc2r"></a>
109 <a name="index-fftw_005fplan_005fguru_005fsplit_005fdft_005fc2r"></a>
110
111 <p>Plan a real-input (r2c) or real-output (c2r), multi-dimensional DFT with
112 transform dimensions given by (<code>rank</code>, <code>dims</code>) over a
113 multi-dimensional vector (loop) of dimensions (<code>howmany_rank</code>,
114 <code>howmany_dims</code>). <code>dims</code> and <code>howmany_dims</code> should point
115 to <code>fftw_iodim</code> arrays of length <code>rank</code> and
116 <code>howmany_rank</code>, respectively. As for the basic and advanced
117 interfaces, an r2c transform is <code>FFTW_FORWARD</code> and a c2r transform
118 is <code>FFTW_BACKWARD</code>.
119 </p>
120 <p>The <em>last</em> dimension of <code>dims</code> is interpreted specially:
121 that dimension of the real array has size <code>dims[rank-1].n</code>, but
122 that dimension of the complex array has size <code>dims[rank-1].n/2+1</code>
123 (division rounded down). The strides, on the other hand, are taken to
124 be exactly as specified. It is up to the user to specify the strides
125 appropriately for the peculiar dimensions of the data, and we do not
126 guarantee that the planner will succeed (return non-<code>NULL</code>) for
127 any dimensions other than those described in <a href="Real_002ddata-DFT-Array-Format.html#Real_002ddata-DFT-Array-Format">Real-data DFT Array Format</a> and generalized in <a href="Advanced-Real_002ddata-DFTs.html#Advanced-Real_002ddata-DFTs">Advanced Real-data DFTs</a>. (That is,
128 for an in-place transform, each individual dimension should be able to
129 operate in place.)
130 <a name="index-in_002dplace-6"></a>
131 </p>
132
133 <p><code>in</code> and <code>out</code> point to the input and output arrays for r2c
134 and c2r transforms, respectively. For split arrays, <code>ri</code> and
135 <code>ii</code> point to the real and imaginary input arrays for a c2r
136 transform, and <code>ro</code> and <code>io</code> point to the real and imaginary
137 output arrays for an r2c transform. <code>in</code> and <code>ro</code> or
138 <code>ri</code> and <code>out</code> may be the same, indicating an in-place
139 transform. (In-place transforms where <code>in</code> and <code>io</code> or
140 <code>ii</code> and <code>out</code> are the same are not currently supported.)
141 </p>
142 <a name="index-flags-6"></a>
143 <p><code>flags</code> is a bitwise OR (&lsquo;<samp>|</samp>&rsquo;) of zero or more planner flags,
144 as defined in <a href="Planner-Flags.html#Planner-Flags">Planner Flags</a>.
145 </p>
146 <p>In-place transforms of rank greater than 1 are currently only
147 supported for interleaved arrays. For split arrays, the planner will
148 return <code>NULL</code>.
149 <a name="index-in_002dplace-7"></a>
150 </p>
151 <hr>
152 <div class="header">
153 <p>
154 Next: <a href="Guru-Real_002dto_002dreal-Transforms.html#Guru-Real_002dto_002dreal-Transforms" accesskey="n" rel="next">Guru Real-to-real Transforms</a>, Previous: <a href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" accesskey="p" rel="prev">Guru Complex DFTs</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>
155 </div>
156
157
158
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