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author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
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3 <title>Advanced Real-data DFTs - FFTW 3.3.3</title>
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51 <p>
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57
58 <h4 class="subsection">4.4.2 Advanced Real-data DFTs</h4>
59
60 <pre class="example"> fftw_plan fftw_plan_many_dft_r2c(int rank, const int *n, int howmany,
61 double *in, const int *inembed,
62 int istride, int idist,
63 fftw_complex *out, const int *onembed,
64 int ostride, int odist,
65 unsigned flags);
66 fftw_plan fftw_plan_many_dft_c2r(int rank, const int *n, int howmany,
67 fftw_complex *in, const int *inembed,
68 int istride, int idist,
69 double *out, const int *onembed,
70 int ostride, int odist,
71 unsigned flags);
72 </pre>
73 <p><a name="index-fftw_005fplan_005fmany_005fdft_005fr2c-236"></a><a name="index-fftw_005fplan_005fmany_005fdft_005fc2r-237"></a>
74 Like <code>fftw_plan_many_dft</code>, these two functions add <code>howmany</code>,
75 <code>nembed</code>, <code>stride</code>, and <code>dist</code> parameters to the
76 <code>fftw_plan_dft_r2c</code> and <code>fftw_plan_dft_c2r</code> functions, but
77 otherwise behave the same as the basic interface.
78
79 <p>The interpretation of <code>howmany</code>, <code>stride</code>, and <code>dist</code> are
80 the same as for <code>fftw_plan_many_dft</code>, above. Note that the
81 <code>stride</code> and <code>dist</code> for the real array are in units of
82 <code>double</code>, and for the complex array are in units of
83 <code>fftw_complex</code>.
84
85 <p>If an <code>nembed</code> parameter is <code>NULL</code>, it is interpreted as what
86 it would be in the basic interface, as described in <a href="Real_002ddata-DFT-Array-Format.html#Real_002ddata-DFT-Array-Format">Real-data DFT Array Format</a>. That is, for the complex array the size is assumed to be
87 the same as <code>n</code>, but with the last dimension cut roughly in half.
88 For the real array, the size is assumed to be <code>n</code> if the transform
89 is out-of-place, or <code>n</code> with the last dimension &ldquo;padded&rdquo; if the
90 transform is in-place.
91
92 <p>If an <code>nembed</code> parameter is non-<code>NULL</code>, it is interpreted as
93 the physical size of the corresponding array, in row-major order, just
94 as for <code>fftw_plan_many_dft</code>. In this case, each dimension of
95 <code>nembed</code> should be <code>&gt;=</code> what it would be in the basic
96 interface (e.g. the halved or padded <code>n</code>).
97
98 <p>Arrays <code>n</code>, <code>inembed</code>, and <code>onembed</code> are not used after
99 this function returns. You can safely free or reuse them.
100
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