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1 <html lang="en">
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2 <head>
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3 <title>Guru Complex DFTs - FFTW 3.3.4</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.3.4">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="Guru-Interface.html#Guru-Interface" title="Guru Interface">
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9 <link rel="prev" href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes" title="Guru vector and transform sizes">
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10 <link rel="next" href="Guru-Real_002ddata-DFTs.html#Guru-Real_002ddata-DFTs" title="Guru Real-data DFTs">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.3.4, 20 September 2013).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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33 -->
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35 <style type="text/css"><!--
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44 span.sansserif { font-family:sans-serif; font-weight:normal; }
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <a name="Guru-Complex-DFTs"></a>
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50 <p>
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51 Next: <a rel="next" accesskey="n" href="Guru-Real_002ddata-DFTs.html#Guru-Real_002ddata-DFTs">Guru Real-data DFTs</a>,
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52 Previous: <a rel="previous" accesskey="p" href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes">Guru vector and transform sizes</a>,
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53 Up: <a rel="up" accesskey="u" href="Guru-Interface.html#Guru-Interface">Guru Interface</a>
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54 <hr>
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55 </div>
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56
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57 <h4 class="subsection">4.5.3 Guru Complex DFTs</h4>
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58
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59 <pre class="example"> fftw_plan fftw_plan_guru_dft(
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60 int rank, const fftw_iodim *dims,
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61 int howmany_rank, const fftw_iodim *howmany_dims,
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62 fftw_complex *in, fftw_complex *out,
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63 int sign, unsigned flags);
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64
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65 fftw_plan fftw_plan_guru_split_dft(
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66 int rank, const fftw_iodim *dims,
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67 int howmany_rank, const fftw_iodim *howmany_dims,
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68 double *ri, double *ii, double *ro, double *io,
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69 unsigned flags);
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70 </pre>
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71 <p><a name="index-fftw_005fplan_005fguru_005fdft-250"></a><a name="index-fftw_005fplan_005fguru_005fsplit_005fdft-251"></a>
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72 These two functions plan a complex-data, multi-dimensional DFT
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73 for the interleaved and split format, respectively.
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74 Transform dimensions are given by (<code>rank</code>, <code>dims</code>) over a
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75 multi-dimensional vector (loop) of dimensions (<code>howmany_rank</code>,
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76 <code>howmany_dims</code>). <code>dims</code> and <code>howmany_dims</code> should point
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77 to <code>fftw_iodim</code> arrays of length <code>rank</code> and
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78 <code>howmany_rank</code>, respectively.
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79
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80 <p><a name="index-flags-252"></a><code>flags</code> is a bitwise OR (‘<samp><span class="samp">|</span></samp>’) of zero or more planner flags,
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81 as defined in <a href="Planner-Flags.html#Planner-Flags">Planner Flags</a>.
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82
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83 <p>In the <code>fftw_plan_guru_dft</code> function, the pointers <code>in</code> and
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84 <code>out</code> point to the interleaved input and output arrays,
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85 respectively. The sign can be either -1 (=
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86 <code>FFTW_FORWARD</code>) or +1 (= <code>FFTW_BACKWARD</code>). If the
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87 pointers are equal, the transform is in-place.
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88
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89 <p>In the <code>fftw_plan_guru_split_dft</code> function,
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90 <code>ri</code> and <code>ii</code> point to the real and imaginary input arrays,
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91 and <code>ro</code> and <code>io</code> point to the real and imaginary output
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92 arrays. The input and output pointers may be the same, indicating an
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93 in-place transform. For example, for <code>fftw_complex</code> pointers
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94 <code>in</code> and <code>out</code>, the corresponding parameters are:
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95
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96 <pre class="example"> ri = (double *) in;
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97 ii = (double *) in + 1;
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98 ro = (double *) out;
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99 io = (double *) out + 1;
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100 </pre>
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101 <p>Because <code>fftw_plan_guru_split_dft</code> accepts split arrays, strides
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102 are expressed in units of <code>double</code>. For a contiguous
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103 <code>fftw_complex</code> array, the overall stride of the transform should
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104 be 2, the distance between consecutive real parts or between
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105 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
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106 real and imaginary parts; real and imaginary arrays with different
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107 strides are not supported.
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108
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109 <p>There is no <code>sign</code> parameter in <code>fftw_plan_guru_split_dft</code>.
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110 This function always plans for an <code>FFTW_FORWARD</code> transform. To
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111 plan for an <code>FFTW_BACKWARD</code> transform, you can exploit the
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112 identity that the backwards DFT is equal to the forwards DFT with the
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113 real and imaginary parts swapped. For example, in the case of the
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114 <code>fftw_complex</code> arrays above, the <code>FFTW_BACKWARD</code> transform
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115 is computed by the parameters:
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116
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117 <pre class="example"> ri = (double *) in + 1;
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118 ii = (double *) in;
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119 ro = (double *) out + 1;
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120 io = (double *) out;
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121 </pre>
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122 <!-- =========> -->
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123 </body></html>
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124
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