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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 (2019-11-19)
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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">
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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.
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Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: Fortran Examples</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: Fortran Examples">
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Chris@82 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@82 36 <link href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" rel="up" title="Calling FFTW from Legacy Fortran">
Chris@82 37 <link href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f" rel="next" title="Wisdom of Fortran?">
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Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Fortran-Examples"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f" accesskey="n" rel="next">Wisdom of Fortran?</a>, Previous: <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran" accesskey="p" rel="prev">FFTW Execution in Fortran</a>, Up: <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" accesskey="u" rel="up">Calling FFTW from Legacy Fortran</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="Fortran-Examples-1"></a>
Chris@82 78 <h3 class="section">8.4 Fortran Examples</h3>
Chris@82 79
Chris@82 80 <p>In C, you might have something like the following to transform a
Chris@82 81 one-dimensional complex array:
Chris@82 82 </p>
Chris@82 83 <div class="example">
Chris@82 84 <pre class="example"> fftw_complex in[N], out[N];
Chris@82 85 fftw_plan plan;
Chris@82 86
Chris@82 87 plan = fftw_plan_dft_1d(N,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
Chris@82 88 fftw_execute(plan);
Chris@82 89 fftw_destroy_plan(plan);
Chris@82 90 </pre></div>
Chris@82 91
Chris@82 92 <p>In Fortran, you would use the following to accomplish the same thing:
Chris@82 93 </p>
Chris@82 94 <div class="example">
Chris@82 95 <pre class="example"> double complex in, out
Chris@82 96 dimension in(N), out(N)
Chris@82 97 integer*8 plan
Chris@82 98
Chris@82 99 call dfftw_plan_dft_1d(plan,N,in,out,FFTW_FORWARD,FFTW_ESTIMATE)
Chris@82 100 call dfftw_execute_dft(plan, in, out)
Chris@82 101 call dfftw_destroy_plan(plan)
Chris@82 102 </pre></div>
Chris@82 103 <a name="index-dfftw_005fplan_005fdft_005f1d"></a>
Chris@82 104 <a name="index-dfftw_005fexecute_005fdft-1"></a>
Chris@82 105 <a name="index-dfftw_005fdestroy_005fplan"></a>
Chris@82 106
Chris@82 107 <p>Notice how all routines are called as Fortran subroutines, and the
Chris@82 108 plan is returned via the first argument to <code>dfftw_plan_dft_1d</code>.
Chris@82 109 Notice also that we changed <code>fftw_execute</code> to
Chris@82 110 <code>dfftw_execute_dft</code> (see <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>). To do
Chris@82 111 the same thing, but using 8 threads in parallel (see <a href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW">Multi-threaded FFTW</a>), you would simply prefix these calls with:
Chris@82 112 </p>
Chris@82 113 <div class="example">
Chris@82 114 <pre class="example"> integer iret
Chris@82 115 call dfftw_init_threads(iret)
Chris@82 116 call dfftw_plan_with_nthreads(8)
Chris@82 117 </pre></div>
Chris@82 118 <a name="index-dfftw_005finit_005fthreads"></a>
Chris@82 119 <a name="index-dfftw_005fplan_005fwith_005fnthreads"></a>
Chris@82 120
Chris@82 121 <p>(You might want to check the value of <code>iret</code>: if it is zero, it
Chris@82 122 indicates an unlikely error during thread initialization.)
Chris@82 123 </p>
Chris@82 124 <p>To transform a three-dimensional array in-place with C, you might do:
Chris@82 125 </p>
Chris@82 126 <div class="example">
Chris@82 127 <pre class="example"> fftw_complex arr[L][M][N];
Chris@82 128 fftw_plan plan;
Chris@82 129
Chris@82 130 plan = fftw_plan_dft_3d(L,M,N, arr,arr,
Chris@82 131 FFTW_FORWARD, FFTW_ESTIMATE);
Chris@82 132 fftw_execute(plan);
Chris@82 133 fftw_destroy_plan(plan);
Chris@82 134 </pre></div>
Chris@82 135
Chris@82 136 <p>In Fortran, you would use this instead:
Chris@82 137 </p>
Chris@82 138 <div class="example">
Chris@82 139 <pre class="example"> double complex arr
Chris@82 140 dimension arr(L,M,N)
Chris@82 141 integer*8 plan
Chris@82 142
Chris@82 143 call dfftw_plan_dft_3d(plan, L,M,N, arr,arr,
Chris@82 144 &amp; FFTW_FORWARD, FFTW_ESTIMATE)
Chris@82 145 call dfftw_execute_dft(plan, arr, arr)
Chris@82 146 call dfftw_destroy_plan(plan)
Chris@82 147 </pre></div>
Chris@82 148 <a name="index-dfftw_005fplan_005fdft_005f3d"></a>
Chris@82 149
Chris@82 150 <p>Note that we pass the array dimensions in the &ldquo;natural&rdquo; order in both C
Chris@82 151 and Fortran.
Chris@82 152 </p>
Chris@82 153 <p>To transform a one-dimensional real array in Fortran, you might do:
Chris@82 154 </p>
Chris@82 155 <div class="example">
Chris@82 156 <pre class="example"> double precision in
Chris@82 157 dimension in(N)
Chris@82 158 double complex out
Chris@82 159 dimension out(N/2 + 1)
Chris@82 160 integer*8 plan
Chris@82 161
Chris@82 162 call dfftw_plan_dft_r2c_1d(plan,N,in,out,FFTW_ESTIMATE)
Chris@82 163 call dfftw_execute_dft_r2c(plan, in, out)
Chris@82 164 call dfftw_destroy_plan(plan)
Chris@82 165 </pre></div>
Chris@82 166 <a name="index-dfftw_005fplan_005fdft_005fr2c_005f1d"></a>
Chris@82 167 <a name="index-dfftw_005fexecute_005fdft_005fr2c"></a>
Chris@82 168
Chris@82 169 <p>To transform a two-dimensional real array, out of place, you might use
Chris@82 170 the following:
Chris@82 171 </p>
Chris@82 172 <div class="example">
Chris@82 173 <pre class="example"> double precision in
Chris@82 174 dimension in(M,N)
Chris@82 175 double complex out
Chris@82 176 dimension out(M/2 + 1, N)
Chris@82 177 integer*8 plan
Chris@82 178
Chris@82 179 call dfftw_plan_dft_r2c_2d(plan,M,N,in,out,FFTW_ESTIMATE)
Chris@82 180 call dfftw_execute_dft_r2c(plan, in, out)
Chris@82 181 call dfftw_destroy_plan(plan)
Chris@82 182 </pre></div>
Chris@82 183 <a name="index-dfftw_005fplan_005fdft_005fr2c_005f2d"></a>
Chris@82 184
Chris@82 185 <p><strong>Important:</strong> Notice that it is the <em>first</em> dimension of the
Chris@82 186 complex output array that is cut in half in Fortran, rather than the
Chris@82 187 last dimension as in C. This is a consequence of the interface routines
Chris@82 188 reversing the order of the array dimensions passed to FFTW so that the
Chris@82 189 Fortran program can use its ordinary column-major order.
Chris@82 190 <a name="index-column_002dmajor-3"></a>
Chris@82 191 <a name="index-r2c_002fc2r-multi_002ddimensional-array-format-3"></a>
Chris@82 192 </p>
Chris@82 193 <hr>
Chris@82 194 <div class="header">
Chris@82 195 <p>
Chris@82 196 Next: <a href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f" accesskey="n" rel="next">Wisdom of Fortran?</a>, Previous: <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran" accesskey="p" rel="prev">FFTW Execution in Fortran</a>, Up: <a href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" accesskey="u" rel="up">Calling FFTW from Legacy Fortran</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@82 197 </div>
Chris@82 198
Chris@82 199
Chris@82 200
Chris@82 201 </body>
Chris@82 202 </html>