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Add FFTW3
author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
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Chris@10 1 <html lang="en">
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Chris@10 3 <title>Advanced Real-data DFTs - FFTW 3.3.3</title>
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Chris@10 48 <div class="node">
Chris@10 49 <a name="Advanced-Real-data-DFTs"></a>
Chris@10 50 <a name="Advanced-Real_002ddata-DFTs"></a>
Chris@10 51 <p>
Chris@10 52 Next:&nbsp;<a rel="next" accesskey="n" href="Advanced-Real_002dto_002dreal-Transforms.html#Advanced-Real_002dto_002dreal-Transforms">Advanced Real-to-real Transforms</a>,
Chris@10 53 Previous:&nbsp;<a rel="previous" accesskey="p" href="Advanced-Complex-DFTs.html#Advanced-Complex-DFTs">Advanced Complex DFTs</a>,
Chris@10 54 Up:&nbsp;<a rel="up" accesskey="u" href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a>
Chris@10 55 <hr>
Chris@10 56 </div>
Chris@10 57
Chris@10 58 <h4 class="subsection">4.4.2 Advanced Real-data DFTs</h4>
Chris@10 59
Chris@10 60 <pre class="example"> fftw_plan fftw_plan_many_dft_r2c(int rank, const int *n, int howmany,
Chris@10 61 double *in, const int *inembed,
Chris@10 62 int istride, int idist,
Chris@10 63 fftw_complex *out, const int *onembed,
Chris@10 64 int ostride, int odist,
Chris@10 65 unsigned flags);
Chris@10 66 fftw_plan fftw_plan_many_dft_c2r(int rank, const int *n, int howmany,
Chris@10 67 fftw_complex *in, const int *inembed,
Chris@10 68 int istride, int idist,
Chris@10 69 double *out, const int *onembed,
Chris@10 70 int ostride, int odist,
Chris@10 71 unsigned flags);
Chris@10 72 </pre>
Chris@10 73 <p><a name="index-fftw_005fplan_005fmany_005fdft_005fr2c-236"></a><a name="index-fftw_005fplan_005fmany_005fdft_005fc2r-237"></a>
Chris@10 74 Like <code>fftw_plan_many_dft</code>, these two functions add <code>howmany</code>,
Chris@10 75 <code>nembed</code>, <code>stride</code>, and <code>dist</code> parameters to the
Chris@10 76 <code>fftw_plan_dft_r2c</code> and <code>fftw_plan_dft_c2r</code> functions, but
Chris@10 77 otherwise behave the same as the basic interface.
Chris@10 78
Chris@10 79 <p>The interpretation of <code>howmany</code>, <code>stride</code>, and <code>dist</code> are
Chris@10 80 the same as for <code>fftw_plan_many_dft</code>, above. Note that the
Chris@10 81 <code>stride</code> and <code>dist</code> for the real array are in units of
Chris@10 82 <code>double</code>, and for the complex array are in units of
Chris@10 83 <code>fftw_complex</code>.
Chris@10 84
Chris@10 85 <p>If an <code>nembed</code> parameter is <code>NULL</code>, it is interpreted as what
Chris@10 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
Chris@10 87 the same as <code>n</code>, but with the last dimension cut roughly in half.
Chris@10 88 For the real array, the size is assumed to be <code>n</code> if the transform
Chris@10 89 is out-of-place, or <code>n</code> with the last dimension &ldquo;padded&rdquo; if the
Chris@10 90 transform is in-place.
Chris@10 91
Chris@10 92 <p>If an <code>nembed</code> parameter is non-<code>NULL</code>, it is interpreted as
Chris@10 93 the physical size of the corresponding array, in row-major order, just
Chris@10 94 as for <code>fftw_plan_many_dft</code>. In this case, each dimension of
Chris@10 95 <code>nembed</code> should be <code>&gt;=</code> what it would be in the basic
Chris@10 96 interface (e.g. the halved or padded <code>n</code>).
Chris@10 97
Chris@10 98 <p>Arrays <code>n</code>, <code>inembed</code>, and <code>onembed</code> are not used after
Chris@10 99 this function returns. You can safely free or reuse them.
Chris@10 100
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Chris@10 103