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Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
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Chris@42 3 <!-- This manual is for FFTW
Chris@42 4 (version 3.3.5, 30 July 2016).
Chris@42 5
Chris@42 6 Copyright (C) 2003 Matteo Frigo.
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Chris@42 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Other Multi-dimensional Real-data MPI Transforms</title>
Chris@42 26
Chris@42 27 <meta name="description" content="FFTW 3.3.5: Other Multi-dimensional Real-data MPI Transforms">
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Chris@42 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@42 36 <link href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" rel="up" title="Distributed-memory FFTW with MPI">
Chris@42 37 <link href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" rel="next" title="FFTW MPI Transposes">
Chris@42 38 <link href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html#Multi_002ddimensional-MPI-DFTs-of-Real-Data" rel="prev" title="Multi-dimensional MPI DFTs of Real Data">
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Chris@42 69 </head>
Chris@42 70
Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="Other-Multi_002ddimensional-Real_002ddata-MPI-Transforms"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 Next: <a href="FFTW-MPI-Transposes.html#FFTW-MPI-Transposes" accesskey="n" rel="next">FFTW MPI Transposes</a>, Previous: <a href="Multi_002ddimensional-MPI-DFTs-of-Real-Data.html#Multi_002ddimensional-MPI-DFTs-of-Real-Data" accesskey="p" rel="prev">Multi-dimensional MPI DFTs of Real Data</a>, Up: <a href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" accesskey="u" rel="up">Distributed-memory FFTW with MPI</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Other-multi_002ddimensional-Real_002dData-MPI-Transforms"></a>
Chris@42 79 <h3 class="section">6.6 Other multi-dimensional Real-Data MPI Transforms</h3>
Chris@42 80
Chris@42 81 <a name="index-r2r-3"></a>
Chris@42 82 <p>FFTW&rsquo;s MPI interface also supports multi-dimensional &lsquo;<samp>r2r</samp>&rsquo;
Chris@42 83 transforms of all kinds supported by the serial interface
Chris@42 84 (e.g. discrete cosine and sine transforms, discrete Hartley
Chris@42 85 transforms, etc.). Only multi-dimensional &lsquo;<samp>r2r</samp>&rsquo; transforms, not
Chris@42 86 one-dimensional transforms, are currently parallelized.
Chris@42 87 </p>
Chris@42 88 <a name="index-fftw_005fr2r_005fkind-1"></a>
Chris@42 89 <p>These are used much like the multidimensional complex DFTs discussed
Chris@42 90 above, except that the data is real rather than complex, and one needs
Chris@42 91 to pass an r2r transform kind (<code>fftw_r2r_kind</code>) for each
Chris@42 92 dimension as in the serial FFTW (see <a href="More-DFTs-of-Real-Data.html#More-DFTs-of-Real-Data">More DFTs of Real Data</a>).
Chris@42 93 </p>
Chris@42 94 <p>For example, one might perform a two-dimensional L&nbsp;&times;&nbsp;M that is
Chris@42 95 an REDFT10 (DCT-II) in the first dimension and an RODFT10 (DST-II) in
Chris@42 96 the second dimension with code like:
Chris@42 97 </p>
Chris@42 98 <div class="example">
Chris@42 99 <pre class="example"> const ptrdiff_t L = ..., M = ...;
Chris@42 100 fftw_plan plan;
Chris@42 101 double *data;
Chris@42 102 ptrdiff_t alloc_local, local_n0, local_0_start, i, j;
Chris@42 103
Chris@42 104 /* <span class="roman">get local data size and allocate</span> */
Chris@42 105 alloc_local = fftw_mpi_local_size_2d(L, M, MPI_COMM_WORLD,
Chris@42 106 &amp;local_n0, &amp;local_0_start);
Chris@42 107 data = fftw_alloc_real(alloc_local);
Chris@42 108
Chris@42 109 /* <span class="roman">create plan for in-place REDFT10 x RODFT10</span> */
Chris@42 110 plan = fftw_mpi_plan_r2r_2d(L, M, data, data, MPI_COMM_WORLD,
Chris@42 111 FFTW_REDFT10, FFTW_RODFT10, FFTW_MEASURE);
Chris@42 112
Chris@42 113 /* <span class="roman">initialize data to some function</span> my_function(x,y) */
Chris@42 114 for (i = 0; i &lt; local_n0; ++i) for (j = 0; j &lt; M; ++j)
Chris@42 115 data[i*M + j] = my_function(local_0_start + i, j);
Chris@42 116
Chris@42 117 /* <span class="roman">compute transforms, in-place, as many times as desired</span> */
Chris@42 118 fftw_execute(plan);
Chris@42 119
Chris@42 120 fftw_destroy_plan(plan);
Chris@42 121 </pre></div>
Chris@42 122
Chris@42 123 <a name="index-fftw_005falloc_005freal-3"></a>
Chris@42 124 <p>Notice that we use the same &lsquo;<samp>local_size</samp>&rsquo; functions as we did for
Chris@42 125 complex data, only now we interpret the sizes in terms of real rather
Chris@42 126 than complex values, and correspondingly use <code>fftw_alloc_real</code>.
Chris@42 127 </p>
Chris@42 128
Chris@42 129
Chris@42 130
Chris@42 131 </body>
Chris@42 132 </html>