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Replace these with versions built using an older toolset (so as to avoid ABI compatibilities when linking on Ubuntu 14.04 for packaging purposes)
author Chris Cannam
date Fri, 07 Feb 2020 11:51:13 +0000
parents d0c2a83c1364
children
rev   line source
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
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Chris@82 22 approved by the Free Software Foundation. -->
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: 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 66
Chris@82 67
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>