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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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Chris@82 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Chris@82 2 <html>
Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
Chris@82 5
Chris@82 6 Copyright (C) 2003 Matteo Frigo.
Chris@82 7
Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
Chris@82 9
Chris@82 10 Permission is granted to make and distribute verbatim copies of this
Chris@82 11 manual provided the copyright notice and this permission notice are
Chris@82 12 preserved on all copies.
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Chris@82 15 manual under the conditions for verbatim copying, provided that the
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Chris@82 23 <!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: 2d MPI example</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: 2d MPI example">
Chris@82 28 <meta name="keywords" content="FFTW 3.3.8: 2d MPI example">
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Chris@82 33 <link href="index.html#Top" rel="start" title="Top">
Chris@82 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
Chris@82 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@82 36 <link href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" rel="up" title="Distributed-memory FFTW with MPI">
Chris@82 37 <link href="MPI-Data-Distribution.html#MPI-Data-Distribution" rel="next" title="MPI Data Distribution">
Chris@82 38 <link href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW" rel="prev" title="Linking and Initializing MPI FFTW">
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Chris@82 66
Chris@82 67
Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="g_t2d-MPI-example"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="MPI-Data-Distribution.html#MPI-Data-Distribution" accesskey="n" rel="next">MPI Data Distribution</a>, Previous: <a href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW" accesskey="p" rel="prev">Linking and Initializing MPI FFTW</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@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="g_t2d-MPI-example-1"></a>
Chris@82 78 <h3 class="section">6.3 2d MPI example</h3>
Chris@82 79
Chris@82 80 <p>Before we document the FFTW MPI interface in detail, we begin with a
Chris@82 81 simple example outlining how one would perform a two-dimensional
Chris@82 82 <code>N0</code> by <code>N1</code> complex DFT.
Chris@82 83 </p>
Chris@82 84 <div class="example">
Chris@82 85 <pre class="example">#include &lt;fftw3-mpi.h&gt;
Chris@82 86
Chris@82 87 int main(int argc, char **argv)
Chris@82 88 {
Chris@82 89 const ptrdiff_t N0 = ..., N1 = ...;
Chris@82 90 fftw_plan plan;
Chris@82 91 fftw_complex *data;
Chris@82 92 ptrdiff_t alloc_local, local_n0, local_0_start, i, j;
Chris@82 93
Chris@82 94 MPI_Init(&amp;argc, &amp;argv);
Chris@82 95 fftw_mpi_init();
Chris@82 96
Chris@82 97 /* <span class="roman">get local data size and allocate</span> */
Chris@82 98 alloc_local = fftw_mpi_local_size_2d(N0, N1, MPI_COMM_WORLD,
Chris@82 99 &amp;local_n0, &amp;local_0_start);
Chris@82 100 data = fftw_alloc_complex(alloc_local);
Chris@82 101
Chris@82 102 /* <span class="roman">create plan for in-place forward DFT</span> */
Chris@82 103 plan = fftw_mpi_plan_dft_2d(N0, N1, data, data, MPI_COMM_WORLD,
Chris@82 104 FFTW_FORWARD, FFTW_ESTIMATE);
Chris@82 105
Chris@82 106 /* <span class="roman">initialize data to some function</span> my_function(x,y) */
Chris@82 107 for (i = 0; i &lt; local_n0; ++i) for (j = 0; j &lt; N1; ++j)
Chris@82 108 data[i*N1 + j] = my_function(local_0_start + i, j);
Chris@82 109
Chris@82 110 /* <span class="roman">compute transforms, in-place, as many times as desired</span> */
Chris@82 111 fftw_execute(plan);
Chris@82 112
Chris@82 113 fftw_destroy_plan(plan);
Chris@82 114
Chris@82 115 MPI_Finalize();
Chris@82 116 }
Chris@82 117 </pre></div>
Chris@82 118
Chris@82 119 <p>As can be seen above, the MPI interface follows the same basic style
Chris@82 120 of allocate/plan/execute/destroy as the serial FFTW routines. All of
Chris@82 121 the MPI-specific routines are prefixed with &lsquo;<samp>fftw_mpi_</samp>&rsquo; instead
Chris@82 122 of &lsquo;<samp>fftw_</samp>&rsquo;. There are a few important differences, however:
Chris@82 123 </p>
Chris@82 124 <p>First, we must call <code>fftw_mpi_init()</code> after calling
Chris@82 125 <code>MPI_Init</code> (required in all MPI programs) and before calling any
Chris@82 126 other &lsquo;<samp>fftw_mpi_</samp>&rsquo; routine.
Chris@82 127 <a name="index-MPI_005fInit"></a>
Chris@82 128 <a name="index-fftw_005fmpi_005finit-1"></a>
Chris@82 129 </p>
Chris@82 130
Chris@82 131 <p>Second, when we create the plan with <code>fftw_mpi_plan_dft_2d</code>,
Chris@82 132 analogous to <code>fftw_plan_dft_2d</code>, we pass an additional argument:
Chris@82 133 the communicator, indicating which processes will participate in the
Chris@82 134 transform (here <code>MPI_COMM_WORLD</code>, indicating all processes).
Chris@82 135 Whenever you create, execute, or destroy a plan for an MPI transform,
Chris@82 136 you must call the corresponding FFTW routine on <em>all</em> processes
Chris@82 137 in the communicator for that transform. (That is, these are
Chris@82 138 <em>collective</em> calls.) Note that the plan for the MPI transform
Chris@82 139 uses the standard <code>fftw_execute</code> and <code>fftw_destroy</code> routines
Chris@82 140 (on the other hand, there are MPI-specific new-array execute functions
Chris@82 141 documented below).
Chris@82 142 <a name="index-collective-function"></a>
Chris@82 143 <a name="index-fftw_005fmpi_005fplan_005fdft_005f2d"></a>
Chris@82 144 <a name="index-MPI_005fCOMM_005fWORLD-1"></a>
Chris@82 145 </p>
Chris@82 146
Chris@82 147 <p>Third, all of the FFTW MPI routines take <code>ptrdiff_t</code> arguments
Chris@82 148 instead of <code>int</code> as for the serial FFTW. <code>ptrdiff_t</code> is a
Chris@82 149 standard C integer type which is (at least) 32 bits wide on a 32-bit
Chris@82 150 machine and 64 bits wide on a 64-bit machine. This is to make it easy
Chris@82 151 to specify very large parallel transforms on a 64-bit machine. (You
Chris@82 152 can specify 64-bit transform sizes in the serial FFTW, too, but only
Chris@82 153 by using the &lsquo;<samp>guru64</samp>&rsquo; planner interface. See <a href="64_002dbit-Guru-Interface.html#g_t64_002dbit-Guru-Interface">64-bit Guru Interface</a>.)
Chris@82 154 <a name="index-ptrdiff_005ft-1"></a>
Chris@82 155 <a name="index-64_002dbit-architecture-1"></a>
Chris@82 156 </p>
Chris@82 157
Chris@82 158 <p>Fourth, and most importantly, you don&rsquo;t allocate the entire
Chris@82 159 two-dimensional array on each process. Instead, you call
Chris@82 160 <code>fftw_mpi_local_size_2d</code> to find out what <em>portion</em> of the
Chris@82 161 array resides on each processor, and how much space to allocate.
Chris@82 162 Here, the portion of the array on each process is a <code>local_n0</code> by
Chris@82 163 <code>N1</code> slice of the total array, starting at index
Chris@82 164 <code>local_0_start</code>. The total number of <code>fftw_complex</code> numbers
Chris@82 165 to allocate is given by the <code>alloc_local</code> return value, which
Chris@82 166 <em>may</em> be greater than <code>local_n0 * N1</code> (in case some
Chris@82 167 intermediate calculations require additional storage). The data
Chris@82 168 distribution in FFTW&rsquo;s MPI interface is described in more detail by
Chris@82 169 the next section.
Chris@82 170 <a name="index-fftw_005fmpi_005flocal_005fsize_005f2d"></a>
Chris@82 171 <a name="index-data-distribution-1"></a>
Chris@82 172 </p>
Chris@82 173
Chris@82 174 <p>Given the portion of the array that resides on the local process, it
Chris@82 175 is straightforward to initialize the data (here to a function
Chris@82 176 <code>myfunction</code>) and otherwise manipulate it. Of course, at the end
Chris@82 177 of the program you may want to output the data somehow, but
Chris@82 178 synchronizing this output is up to you and is beyond the scope of this
Chris@82 179 manual. (One good way to output a large multi-dimensional distributed
Chris@82 180 array in MPI to a portable binary file is to use the free HDF5
Chris@82 181 library; see the <a href="http://www.hdfgroup.org/">HDF home page</a>.)
Chris@82 182 <a name="index-HDF5"></a>
Chris@82 183 <a name="index-MPI-I_002fO"></a>
Chris@82 184 </p>
Chris@82 185 <hr>
Chris@82 186 <div class="header">
Chris@82 187 <p>
Chris@82 188 Next: <a href="MPI-Data-Distribution.html#MPI-Data-Distribution" accesskey="n" rel="next">MPI Data Distribution</a>, Previous: <a href="Linking-and-Initializing-MPI-FFTW.html#Linking-and-Initializing-MPI-FFTW" accesskey="p" rel="prev">Linking and Initializing MPI FFTW</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@82 189 </div>
Chris@82 190
Chris@82 191
Chris@82 192
Chris@82 193 </body>
Chris@82 194 </html>