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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 2cd0e3b3e1fd
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Chris@42 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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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.
Chris@42 7
Chris@42 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@42 23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Fortran Examples</title>
Chris@42 26
Chris@42 27 <meta name="description" content="FFTW 3.3.5: Fortran Examples">
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Chris@42 36 <link href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" rel="up" title="Calling FFTW from Legacy Fortran">
Chris@42 37 <link href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f" rel="next" title="Wisdom of Fortran?">
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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="Fortran-Examples"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 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@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Fortran-Examples-1"></a>
Chris@42 79 <h3 class="section">8.4 Fortran Examples</h3>
Chris@42 80
Chris@42 81 <p>In C, you might have something like the following to transform a
Chris@42 82 one-dimensional complex array:
Chris@42 83 </p>
Chris@42 84 <div class="example">
Chris@42 85 <pre class="example"> fftw_complex in[N], out[N];
Chris@42 86 fftw_plan plan;
Chris@42 87
Chris@42 88 plan = fftw_plan_dft_1d(N,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
Chris@42 89 fftw_execute(plan);
Chris@42 90 fftw_destroy_plan(plan);
Chris@42 91 </pre></div>
Chris@42 92
Chris@42 93 <p>In Fortran, you would use the following to accomplish the same thing:
Chris@42 94 </p>
Chris@42 95 <div class="example">
Chris@42 96 <pre class="example"> double complex in, out
Chris@42 97 dimension in(N), out(N)
Chris@42 98 integer*8 plan
Chris@42 99
Chris@42 100 call dfftw_plan_dft_1d(plan,N,in,out,FFTW_FORWARD,FFTW_ESTIMATE)
Chris@42 101 call dfftw_execute_dft(plan, in, out)
Chris@42 102 call dfftw_destroy_plan(plan)
Chris@42 103 </pre></div>
Chris@42 104 <a name="index-dfftw_005fplan_005fdft_005f1d"></a>
Chris@42 105 <a name="index-dfftw_005fexecute_005fdft-1"></a>
Chris@42 106 <a name="index-dfftw_005fdestroy_005fplan"></a>
Chris@42 107
Chris@42 108 <p>Notice how all routines are called as Fortran subroutines, and the
Chris@42 109 plan is returned via the first argument to <code>dfftw_plan_dft_1d</code>.
Chris@42 110 Notice also that we changed <code>fftw_execute</code> to
Chris@42 111 <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@42 112 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@42 113 </p>
Chris@42 114 <div class="example">
Chris@42 115 <pre class="example"> integer iret
Chris@42 116 call dfftw_init_threads(iret)
Chris@42 117 call dfftw_plan_with_nthreads(8)
Chris@42 118 </pre></div>
Chris@42 119 <a name="index-dfftw_005finit_005fthreads"></a>
Chris@42 120 <a name="index-dfftw_005fplan_005fwith_005fnthreads"></a>
Chris@42 121
Chris@42 122 <p>(You might want to check the value of <code>iret</code>: if it is zero, it
Chris@42 123 indicates an unlikely error during thread initialization.)
Chris@42 124 </p>
Chris@42 125 <p>To transform a three-dimensional array in-place with C, you might do:
Chris@42 126 </p>
Chris@42 127 <div class="example">
Chris@42 128 <pre class="example"> fftw_complex arr[L][M][N];
Chris@42 129 fftw_plan plan;
Chris@42 130
Chris@42 131 plan = fftw_plan_dft_3d(L,M,N, arr,arr,
Chris@42 132 FFTW_FORWARD, FFTW_ESTIMATE);
Chris@42 133 fftw_execute(plan);
Chris@42 134 fftw_destroy_plan(plan);
Chris@42 135 </pre></div>
Chris@42 136
Chris@42 137 <p>In Fortran, you would use this instead:
Chris@42 138 </p>
Chris@42 139 <div class="example">
Chris@42 140 <pre class="example"> double complex arr
Chris@42 141 dimension arr(L,M,N)
Chris@42 142 integer*8 plan
Chris@42 143
Chris@42 144 call dfftw_plan_dft_3d(plan, L,M,N, arr,arr,
Chris@42 145 &amp; FFTW_FORWARD, FFTW_ESTIMATE)
Chris@42 146 call dfftw_execute_dft(plan, arr, arr)
Chris@42 147 call dfftw_destroy_plan(plan)
Chris@42 148 </pre></div>
Chris@42 149 <a name="index-dfftw_005fplan_005fdft_005f3d"></a>
Chris@42 150
Chris@42 151 <p>Note that we pass the array dimensions in the &ldquo;natural&rdquo; order in both C
Chris@42 152 and Fortran.
Chris@42 153 </p>
Chris@42 154 <p>To transform a one-dimensional real array in Fortran, you might do:
Chris@42 155 </p>
Chris@42 156 <div class="example">
Chris@42 157 <pre class="example"> double precision in
Chris@42 158 dimension in(N)
Chris@42 159 double complex out
Chris@42 160 dimension out(N/2 + 1)
Chris@42 161 integer*8 plan
Chris@42 162
Chris@42 163 call dfftw_plan_dft_r2c_1d(plan,N,in,out,FFTW_ESTIMATE)
Chris@42 164 call dfftw_execute_dft_r2c(plan, in, out)
Chris@42 165 call dfftw_destroy_plan(plan)
Chris@42 166 </pre></div>
Chris@42 167 <a name="index-dfftw_005fplan_005fdft_005fr2c_005f1d"></a>
Chris@42 168 <a name="index-dfftw_005fexecute_005fdft_005fr2c"></a>
Chris@42 169
Chris@42 170 <p>To transform a two-dimensional real array, out of place, you might use
Chris@42 171 the following:
Chris@42 172 </p>
Chris@42 173 <div class="example">
Chris@42 174 <pre class="example"> double precision in
Chris@42 175 dimension in(M,N)
Chris@42 176 double complex out
Chris@42 177 dimension out(M/2 + 1, N)
Chris@42 178 integer*8 plan
Chris@42 179
Chris@42 180 call dfftw_plan_dft_r2c_2d(plan,M,N,in,out,FFTW_ESTIMATE)
Chris@42 181 call dfftw_execute_dft_r2c(plan, in, out)
Chris@42 182 call dfftw_destroy_plan(plan)
Chris@42 183 </pre></div>
Chris@42 184 <a name="index-dfftw_005fplan_005fdft_005fr2c_005f2d"></a>
Chris@42 185
Chris@42 186 <p><strong>Important:</strong> Notice that it is the <em>first</em> dimension of the
Chris@42 187 complex output array that is cut in half in Fortran, rather than the
Chris@42 188 last dimension as in C. This is a consequence of the interface routines
Chris@42 189 reversing the order of the array dimensions passed to FFTW so that the
Chris@42 190 Fortran program can use its ordinary column-major order.
Chris@42 191 <a name="index-column_002dmajor-3"></a>
Chris@42 192 <a name="index-r2c_002fc2r-multi_002ddimensional-array-format-3"></a>
Chris@42 193 </p>
Chris@42 194 <hr>
Chris@42 195 <div class="header">
Chris@42 196 <p>
Chris@42 197 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@42 198 </div>
Chris@42 199
Chris@42 200
Chris@42 201
Chris@42 202 </body>
Chris@42 203 </html>