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6.8 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This manual is for FFTW
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(version 3.3.10, 10 December 2020).
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Copyright (C) 2003 Matteo Frigo.
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Copyright (C) 2003 Massachusetts Institute of Technology.
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Permission is granted to make and distribute verbatim copies of this
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manual provided the copyright notice and this permission notice are
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preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided that the
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entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions,
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except that this permission notice may be stated in a translation
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approved by the Free Software Foundation. -->
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<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Guru Complex DFTs (FFTW 3.3.10)</title>
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<meta name="description" content="Guru Complex DFTs (FFTW 3.3.10)">
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<meta name="keywords" content="Guru Complex DFTs (FFTW 3.3.10)">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Guru-Interface.html" rel="up" title="Guru Interface">
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<link href="Guru-Real_002ddata-DFTs.html" rel="next" title="Guru Real-data DFTs">
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<link href="Guru-vector-and-transform-sizes.html" rel="prev" title="Guru vector and transform sizes">
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</head>
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<body lang="en">
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<span id="Guru-Complex-DFTs"></span><div class="header">
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<p>
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Next: <a href="Guru-Real_002ddata-DFTs.html" accesskey="n" rel="next">Guru Real-data DFTs</a>, Previous: <a href="Guru-vector-and-transform-sizes.html" accesskey="p" rel="prev">Guru vector and transform sizes</a>, Up: <a href="Guru-Interface.html" accesskey="u" rel="up">Guru Interface</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<span id="Guru-Complex-DFTs-1"></span><h4 class="subsection">4.5.3 Guru Complex DFTs</h4>
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<div class="example">
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<pre class="example">fftw_plan fftw_plan_guru_dft(
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int rank, const fftw_iodim *dims,
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int howmany_rank, const fftw_iodim *howmany_dims,
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fftw_complex *in, fftw_complex *out,
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int sign, unsigned flags);
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fftw_plan fftw_plan_guru_split_dft(
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int rank, const fftw_iodim *dims,
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int howmany_rank, const fftw_iodim *howmany_dims,
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double *ri, double *ii, double *ro, double *io,
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unsigned flags);
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</pre></div>
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<span id="index-fftw_005fplan_005fguru_005fdft"></span>
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<span id="index-fftw_005fplan_005fguru_005fsplit_005fdft"></span>
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<p>These two functions plan a complex-data, multi-dimensional DFT
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for the interleaved and split format, respectively.
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Transform dimensions are given by (<code>rank</code>, <code>dims</code>) over a
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multi-dimensional vector (loop) of dimensions (<code>howmany_rank</code>,
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<code>howmany_dims</code>). <code>dims</code> and <code>howmany_dims</code> should point
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to <code>fftw_iodim</code> arrays of length <code>rank</code> and
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<code>howmany_rank</code>, respectively.
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</p>
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<span id="index-flags-5"></span>
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<p><code>flags</code> is a bitwise OR (‘<samp>|</samp>’) of zero or more planner flags,
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as defined in <a href="Planner-Flags.html">Planner Flags</a>.
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</p>
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<p>In the <code>fftw_plan_guru_dft</code> function, the pointers <code>in</code> and
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<code>out</code> point to the interleaved input and output arrays,
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respectively. The sign can be either <em>-1</em> (=
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<code>FFTW_FORWARD</code>) or <em>+1</em> (= <code>FFTW_BACKWARD</code>). If the
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pointers are equal, the transform is in-place.
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</p>
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<p>In the <code>fftw_plan_guru_split_dft</code> function,
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<code>ri</code> and <code>ii</code> point to the real and imaginary input arrays,
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and <code>ro</code> and <code>io</code> point to the real and imaginary output
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arrays. The input and output pointers may be the same, indicating an
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in-place transform. For example, for <code>fftw_complex</code> pointers
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<code>in</code> and <code>out</code>, the corresponding parameters are:
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</p>
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<div class="example">
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<pre class="example">ri = (double *) in;
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ii = (double *) in + 1;
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ro = (double *) out;
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io = (double *) out + 1;
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</pre></div>
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<p>Because <code>fftw_plan_guru_split_dft</code> accepts split arrays, strides
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are expressed in units of <code>double</code>. For a contiguous
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<code>fftw_complex</code> array, the overall stride of the transform should
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be 2, the distance between consecutive real parts or between
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consecutive imaginary parts; see <a href="Guru-vector-and-transform-sizes.html">Guru vector and transform sizes</a>. Note that the dimension strides are applied equally to the
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real and imaginary parts; real and imaginary arrays with different
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strides are not supported.
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</p>
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<p>There is no <code>sign</code> parameter in <code>fftw_plan_guru_split_dft</code>.
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This function always plans for an <code>FFTW_FORWARD</code> transform. To
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plan for an <code>FFTW_BACKWARD</code> transform, you can exploit the
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identity that the backwards DFT is equal to the forwards DFT with the
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real and imaginary parts swapped. For example, in the case of the
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<code>fftw_complex</code> arrays above, the <code>FFTW_BACKWARD</code> transform
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is computed by the parameters:
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</p>
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<div class="example">
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<pre class="example">ri = (double *) in + 1;
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ii = (double *) in;
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ro = (double *) out + 1;
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io = (double *) out;
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</pre></div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Guru-Real_002ddata-DFTs.html" accesskey="n" rel="next">Guru Real-data DFTs</a>, Previous: <a href="Guru-vector-and-transform-sizes.html" accesskey="p" rel="prev">Guru vector and transform sizes</a>, Up: <a href="Guru-Interface.html" accesskey="u" rel="up">Guru Interface</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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