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121 lines
5.5 KiB
HTML
<!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>Other Multi-dimensional Real-data MPI Transforms (FFTW 3.3.10)</title>
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<meta name="description" content="Other Multi-dimensional Real-data MPI Transforms (FFTW 3.3.10)">
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<meta name="keywords" content="Other Multi-dimensional Real-data MPI Transforms (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="Distributed_002dmemory-FFTW-with-MPI.html" rel="up" title="Distributed-memory FFTW with MPI">
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<link href="FFTW-MPI-Transposes.html" rel="next" title="FFTW MPI Transposes">
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<link href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html" rel="prev" title="Multi-dimensional MPI DFTs of Real Data">
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</head>
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<body lang="en">
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<span id="Other-Multi_002ddimensional-Real_002ddata-MPI-Transforms"></span><div class="header">
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<p>
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Next: <a href="FFTW-MPI-Transposes.html" accesskey="n" rel="next">FFTW MPI Transposes</a>, Previous: <a href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html" accesskey="p" rel="prev">Multi-dimensional MPI DFTs of Real Data</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html" accesskey="u" rel="up">Distributed-memory FFTW with MPI</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="Other-multi_002ddimensional-Real_002dData-MPI-Transforms"></span><h3 class="section">6.6 Other multi-dimensional Real-Data MPI Transforms</h3>
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<span id="index-r2r-3"></span>
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<p>FFTW’s MPI interface also supports multi-dimensional ‘<samp>r2r</samp>’
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transforms of all kinds supported by the serial interface
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(e.g. discrete cosine and sine transforms, discrete Hartley
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transforms, etc.). Only multi-dimensional ‘<samp>r2r</samp>’ transforms, not
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one-dimensional transforms, are currently parallelized.
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</p>
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<span id="index-fftw_005fr2r_005fkind-1"></span>
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<p>These are used much like the multidimensional complex DFTs discussed
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above, except that the data is real rather than complex, and one needs
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to pass an r2r transform kind (<code>fftw_r2r_kind</code>) for each
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dimension as in the serial FFTW (see <a href="More-DFTs-of-Real-Data.html">More DFTs of Real Data</a>).
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</p>
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<p>For example, one might perform a two-dimensional L × M
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that is
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an REDFT10 (DCT-II) in the first dimension and an RODFT10 (DST-II) in
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the second dimension with code like:
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</p>
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<div class="example">
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<pre class="example"> const ptrdiff_t L = ..., M = ...;
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fftw_plan plan;
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double *data;
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ptrdiff_t alloc_local, local_n0, local_0_start, i, j;
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/* <span class="roman">get local data size and allocate</span> */
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alloc_local = fftw_mpi_local_size_2d(L, M, MPI_COMM_WORLD,
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&local_n0, &local_0_start);
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data = fftw_alloc_real(alloc_local);
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/* <span class="roman">create plan for in-place REDFT10 x RODFT10</span> */
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plan = fftw_mpi_plan_r2r_2d(L, M, data, data, MPI_COMM_WORLD,
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FFTW_REDFT10, FFTW_RODFT10, FFTW_MEASURE);
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/* <span class="roman">initialize data to some function</span> my_function(x,y) */
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for (i = 0; i < local_n0; ++i) for (j = 0; j < M; ++j)
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data[i*M + j] = my_function(local_0_start + i, j);
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/* <span class="roman">compute transforms, in-place, as many times as desired</span> */
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fftw_execute(plan);
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fftw_destroy_plan(plan);
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</pre></div>
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<span id="index-fftw_005falloc_005freal-3"></span>
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<p>Notice that we use the same ‘<samp>local_size</samp>’ functions as we did for
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complex data, only now we interpret the sizes in terms of real rather
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than complex values, and correspondingly use <code>fftw_alloc_real</code>.
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</p>
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</body>
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</html>
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