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Add null config files
author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
parents 7867fa7e1b6b
children
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cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
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cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: Fortran Examples</title>
cannam@127 26
cannam@127 27 <meta name="description" content="FFTW 3.3.5: Fortran Examples">
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cannam@127 36 <link href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" rel="up" title="Calling FFTW from Legacy Fortran">
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cannam@127 70
cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="Fortran-Examples"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="Fortran-Examples-1"></a>
cannam@127 79 <h3 class="section">8.4 Fortran Examples</h3>
cannam@127 80
cannam@127 81 <p>In C, you might have something like the following to transform a
cannam@127 82 one-dimensional complex array:
cannam@127 83 </p>
cannam@127 84 <div class="example">
cannam@127 85 <pre class="example"> fftw_complex in[N], out[N];
cannam@127 86 fftw_plan plan;
cannam@127 87
cannam@127 88 plan = fftw_plan_dft_1d(N,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
cannam@127 89 fftw_execute(plan);
cannam@127 90 fftw_destroy_plan(plan);
cannam@127 91 </pre></div>
cannam@127 92
cannam@127 93 <p>In Fortran, you would use the following to accomplish the same thing:
cannam@127 94 </p>
cannam@127 95 <div class="example">
cannam@127 96 <pre class="example"> double complex in, out
cannam@127 97 dimension in(N), out(N)
cannam@127 98 integer*8 plan
cannam@127 99
cannam@127 100 call dfftw_plan_dft_1d(plan,N,in,out,FFTW_FORWARD,FFTW_ESTIMATE)
cannam@127 101 call dfftw_execute_dft(plan, in, out)
cannam@127 102 call dfftw_destroy_plan(plan)
cannam@127 103 </pre></div>
cannam@127 104 <a name="index-dfftw_005fplan_005fdft_005f1d"></a>
cannam@127 105 <a name="index-dfftw_005fexecute_005fdft-1"></a>
cannam@127 106 <a name="index-dfftw_005fdestroy_005fplan"></a>
cannam@127 107
cannam@127 108 <p>Notice how all routines are called as Fortran subroutines, and the
cannam@127 109 plan is returned via the first argument to <code>dfftw_plan_dft_1d</code>.
cannam@127 110 Notice also that we changed <code>fftw_execute</code> to
cannam@127 111 <code>dfftw_execute_dft</code> (see <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>). To do
cannam@127 112 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:
cannam@127 113 </p>
cannam@127 114 <div class="example">
cannam@127 115 <pre class="example"> integer iret
cannam@127 116 call dfftw_init_threads(iret)
cannam@127 117 call dfftw_plan_with_nthreads(8)
cannam@127 118 </pre></div>
cannam@127 119 <a name="index-dfftw_005finit_005fthreads"></a>
cannam@127 120 <a name="index-dfftw_005fplan_005fwith_005fnthreads"></a>
cannam@127 121
cannam@127 122 <p>(You might want to check the value of <code>iret</code>: if it is zero, it
cannam@127 123 indicates an unlikely error during thread initialization.)
cannam@127 124 </p>
cannam@127 125 <p>To transform a three-dimensional array in-place with C, you might do:
cannam@127 126 </p>
cannam@127 127 <div class="example">
cannam@127 128 <pre class="example"> fftw_complex arr[L][M][N];
cannam@127 129 fftw_plan plan;
cannam@127 130
cannam@127 131 plan = fftw_plan_dft_3d(L,M,N, arr,arr,
cannam@127 132 FFTW_FORWARD, FFTW_ESTIMATE);
cannam@127 133 fftw_execute(plan);
cannam@127 134 fftw_destroy_plan(plan);
cannam@127 135 </pre></div>
cannam@127 136
cannam@127 137 <p>In Fortran, you would use this instead:
cannam@127 138 </p>
cannam@127 139 <div class="example">
cannam@127 140 <pre class="example"> double complex arr
cannam@127 141 dimension arr(L,M,N)
cannam@127 142 integer*8 plan
cannam@127 143
cannam@127 144 call dfftw_plan_dft_3d(plan, L,M,N, arr,arr,
cannam@127 145 &amp; FFTW_FORWARD, FFTW_ESTIMATE)
cannam@127 146 call dfftw_execute_dft(plan, arr, arr)
cannam@127 147 call dfftw_destroy_plan(plan)
cannam@127 148 </pre></div>
cannam@127 149 <a name="index-dfftw_005fplan_005fdft_005f3d"></a>
cannam@127 150
cannam@127 151 <p>Note that we pass the array dimensions in the &ldquo;natural&rdquo; order in both C
cannam@127 152 and Fortran.
cannam@127 153 </p>
cannam@127 154 <p>To transform a one-dimensional real array in Fortran, you might do:
cannam@127 155 </p>
cannam@127 156 <div class="example">
cannam@127 157 <pre class="example"> double precision in
cannam@127 158 dimension in(N)
cannam@127 159 double complex out
cannam@127 160 dimension out(N/2 + 1)
cannam@127 161 integer*8 plan
cannam@127 162
cannam@127 163 call dfftw_plan_dft_r2c_1d(plan,N,in,out,FFTW_ESTIMATE)
cannam@127 164 call dfftw_execute_dft_r2c(plan, in, out)
cannam@127 165 call dfftw_destroy_plan(plan)
cannam@127 166 </pre></div>
cannam@127 167 <a name="index-dfftw_005fplan_005fdft_005fr2c_005f1d"></a>
cannam@127 168 <a name="index-dfftw_005fexecute_005fdft_005fr2c"></a>
cannam@127 169
cannam@127 170 <p>To transform a two-dimensional real array, out of place, you might use
cannam@127 171 the following:
cannam@127 172 </p>
cannam@127 173 <div class="example">
cannam@127 174 <pre class="example"> double precision in
cannam@127 175 dimension in(M,N)
cannam@127 176 double complex out
cannam@127 177 dimension out(M/2 + 1, N)
cannam@127 178 integer*8 plan
cannam@127 179
cannam@127 180 call dfftw_plan_dft_r2c_2d(plan,M,N,in,out,FFTW_ESTIMATE)
cannam@127 181 call dfftw_execute_dft_r2c(plan, in, out)
cannam@127 182 call dfftw_destroy_plan(plan)
cannam@127 183 </pre></div>
cannam@127 184 <a name="index-dfftw_005fplan_005fdft_005fr2c_005f2d"></a>
cannam@127 185
cannam@127 186 <p><strong>Important:</strong> Notice that it is the <em>first</em> dimension of the
cannam@127 187 complex output array that is cut in half in Fortran, rather than the
cannam@127 188 last dimension as in C. This is a consequence of the interface routines
cannam@127 189 reversing the order of the array dimensions passed to FFTW so that the
cannam@127 190 Fortran program can use its ordinary column-major order.
cannam@127 191 <a name="index-column_002dmajor-3"></a>
cannam@127 192 <a name="index-r2c_002fc2r-multi_002ddimensional-array-format-3"></a>
cannam@127 193 </p>
cannam@127 194 <hr>
cannam@127 195 <div class="header">
cannam@127 196 <p>
cannam@127 197 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>
cannam@127 198 </div>
cannam@127 199
cannam@127 200
cannam@127 201
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cannam@127 203 </html>