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