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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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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Guru Real-data DFTs (FFTW 3.3.10)</title>
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<meta name="description" content="Guru Real-data DFTs (FFTW 3.3.10)">
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<meta name="keywords" content="Guru Real-data DFTs (FFTW 3.3.10)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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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_002dto_002dreal-Transforms.html" rel="next" title="Guru Real-to-real Transforms">
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<link href="Guru-Complex-DFTs.html" rel="prev" title="Guru Complex DFTs">
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</head>
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<body lang="en">
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<span id="Guru-Real_002ddata-DFTs"></span><div class="header">
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<p>
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Next: <a href="Guru-Real_002dto_002dreal-Transforms.html" accesskey="n" rel="next">Guru Real-to-real Transforms</a>, Previous: <a href="Guru-Complex-DFTs.html" accesskey="p" rel="prev">Guru Complex DFTs</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-Real_002ddata-DFTs-1"></span><h4 class="subsection">4.5.4 Guru Real-data DFTs</h4>
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<div class="example">
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<pre class="example">fftw_plan fftw_plan_guru_dft_r2c(
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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 *in, fftw_complex *out,
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unsigned flags);
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fftw_plan fftw_plan_guru_split_dft_r2c(
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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 *in, double *ro, double *io,
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unsigned flags);
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fftw_plan fftw_plan_guru_dft_c2r(
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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, double *out,
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unsigned flags);
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fftw_plan fftw_plan_guru_split_dft_c2r(
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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 *out,
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unsigned flags);
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</pre></div>
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<span id="index-fftw_005fplan_005fguru_005fdft_005fr2c"></span>
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<span id="index-fftw_005fplan_005fguru_005fsplit_005fdft_005fr2c"></span>
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<span id="index-fftw_005fplan_005fguru_005fdft_005fc2r"></span>
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<span id="index-fftw_005fplan_005fguru_005fsplit_005fdft_005fc2r"></span>
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<p>Plan a real-input (r2c) or real-output (c2r), multi-dimensional DFT with
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transform dimensions 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. As for the basic and advanced
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interfaces, an r2c transform is <code>FFTW_FORWARD</code> and a c2r transform
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is <code>FFTW_BACKWARD</code>.
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</p>
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<p>The <em>last</em> dimension of <code>dims</code> is interpreted specially:
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that dimension of the real array has size <code>dims[rank-1].n</code>, but
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that dimension of the complex array has size <code>dims[rank-1].n/2+1</code>
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(division rounded down). The strides, on the other hand, are taken to
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be exactly as specified. It is up to the user to specify the strides
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appropriately for the peculiar dimensions of the data, and we do not
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guarantee that the planner will succeed (return non-<code>NULL</code>) for
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any dimensions other than those described in <a href="Real_002ddata-DFT-Array-Format.html">Real-data DFT Array Format</a> and generalized in <a href="Advanced-Real_002ddata-DFTs.html">Advanced Real-data DFTs</a>. (That is,
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for an in-place transform, each individual dimension should be able to
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operate in place.)
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<span id="index-in_002dplace-6"></span>
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</p>
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<p><code>in</code> and <code>out</code> point to the input and output arrays for r2c
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and c2r transforms, respectively. For split arrays, <code>ri</code> and
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<code>ii</code> point to the real and imaginary input arrays for a c2r
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transform, and <code>ro</code> and <code>io</code> point to the real and imaginary
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output arrays for an r2c transform. <code>in</code> and <code>ro</code> or
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<code>ri</code> and <code>out</code> may be the same, indicating an in-place
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transform. (In-place transforms where <code>in</code> and <code>io</code> or
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<code>ii</code> and <code>out</code> are the same are not currently supported.)
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</p>
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<span id="index-flags-6"></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-place transforms of rank greater than 1 are currently only
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supported for interleaved arrays. For split arrays, the planner will
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return <code>NULL</code>.
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<span id="index-in_002dplace-7"></span>
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</p>
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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_002dto_002dreal-Transforms.html" accesskey="n" rel="next">Guru Real-to-real Transforms</a>, Previous: <a href="Guru-Complex-DFTs.html" accesskey="p" rel="prev">Guru Complex DFTs</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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