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