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date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>Guru Complex DFTs - FFTW 3.3.3</title>
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49 <a name="Guru-Complex-DFTs"></a>
50 <p>
51 Next:&nbsp;<a rel="next" accesskey="n" href="Guru-Real_002ddata-DFTs.html#Guru-Real_002ddata-DFTs">Guru Real-data DFTs</a>,
52 Previous:&nbsp;<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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55 </div>
56
57 <h4 class="subsection">4.5.3 Guru Complex DFTs</h4>
58
59 <pre class="example"> fftw_plan fftw_plan_guru_dft(
60 int rank, const fftw_iodim *dims,
61 int howmany_rank, const fftw_iodim *howmany_dims,
62 fftw_complex *in, fftw_complex *out,
63 int sign, unsigned flags);
64
65 fftw_plan fftw_plan_guru_split_dft(
66 int rank, const fftw_iodim *dims,
67 int howmany_rank, const fftw_iodim *howmany_dims,
68 double *ri, double *ii, double *ro, double *io,
69 unsigned flags);
70 </pre>
71 <p><a name="index-fftw_005fplan_005fguru_005fdft-248"></a><a name="index-fftw_005fplan_005fguru_005fsplit_005fdft-249"></a>
72 These two functions plan a complex-data, multi-dimensional DFT
73 for the interleaved and split format, respectively.
74 Transform dimensions are given by (<code>rank</code>, <code>dims</code>) over a
75 multi-dimensional vector (loop) of dimensions (<code>howmany_rank</code>,
76 <code>howmany_dims</code>). <code>dims</code> and <code>howmany_dims</code> should point
77 to <code>fftw_iodim</code> arrays of length <code>rank</code> and
78 <code>howmany_rank</code>, respectively.
79
80 <p><a name="index-flags-250"></a><code>flags</code> is a bitwise OR (&lsquo;<samp><span class="samp">|</span></samp>&rsquo;) of zero or more planner flags,
81 as defined in <a href="Planner-Flags.html#Planner-Flags">Planner Flags</a>.
82
83 <p>In the <code>fftw_plan_guru_dft</code> function, the pointers <code>in</code> and
84 <code>out</code> point to the interleaved input and output arrays,
85 respectively. The sign can be either -1 (=
86 <code>FFTW_FORWARD</code>) or +1 (= <code>FFTW_BACKWARD</code>). If the
87 pointers are equal, the transform is in-place.
88
89 <p>In the <code>fftw_plan_guru_split_dft</code> function,
90 <code>ri</code> and <code>ii</code> point to the real and imaginary input arrays,
91 and <code>ro</code> and <code>io</code> point to the real and imaginary output
92 arrays. The input and output pointers may be the same, indicating an
93 in-place transform. For example, for <code>fftw_complex</code> pointers
94 <code>in</code> and <code>out</code>, the corresponding parameters are:
95
96 <pre class="example"> ri = (double *) in;
97 ii = (double *) in + 1;
98 ro = (double *) out;
99 io = (double *) out + 1;
100 </pre>
101 <p>Because <code>fftw_plan_guru_split_dft</code> accepts split arrays, strides
102 are expressed in units of <code>double</code>. For a contiguous
103 <code>fftw_complex</code> array, the overall stride of the transform should
104 be 2, the distance between consecutive real parts or between
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
106 real and imaginary parts; real and imaginary arrays with different
107 strides are not supported.
108
109 <p>There is no <code>sign</code> parameter in <code>fftw_plan_guru_split_dft</code>.
110 This function always plans for an <code>FFTW_FORWARD</code> transform. To
111 plan for an <code>FFTW_BACKWARD</code> transform, you can exploit the
112 identity that the backwards DFT is equal to the forwards DFT with the
113 real and imaginary parts swapped. For example, in the case of the
114 <code>fftw_complex</code> arrays above, the <code>FFTW_BACKWARD</code> transform
115 is computed by the parameters:
116
117 <pre class="example"> ri = (double *) in + 1;
118 ii = (double *) in;
119 ro = (double *) out + 1;
120 io = (double *) out;
121 </pre>
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