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Vectorised most things to make lifer easier. Still no debug version though. Weird.
author Geogaddi\David <d.m.ronan@qmul.ac.uk>
date Fri, 10 Jul 2015 03:04:11 +0100
parents 25bf17994ef1
children
rev   line source
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d@0 3 <title>Fortran Examples - FFTW 3.2.1</title>
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d@0 13 This manual is for FFTW
d@0 14 (version 3.2.1, 5 February 2009).
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d@0 16 Copyright (C) 2003 Matteo Frigo.
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d@0 48 <div class="node">
d@0 49 <p>
d@0 50 <a name="Fortran-Examples"></a>
d@0 51 Next:&nbsp;<a rel="next" accesskey="n" href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f">Wisdom of Fortran?</a>,
d@0 52 Previous:&nbsp;<a rel="previous" accesskey="p" href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>,
d@0 53 Up:&nbsp;<a rel="up" accesskey="u" href="Calling-FFTW-from-Fortran.html#Calling-FFTW-from-Fortran">Calling FFTW from Fortran</a>
d@0 54 <hr>
d@0 55 </div>
d@0 56
d@0 57 <h3 class="section">7.4 Fortran Examples</h3>
d@0 58
d@0 59 <p>In C, you might have something like the following to transform a
d@0 60 one-dimensional complex array:
d@0 61
d@0 62 <pre class="example"> fftw_complex in[N], out[N];
d@0 63 fftw_plan plan;
d@0 64
d@0 65 plan = fftw_plan_dft_1d(N,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
d@0 66 fftw_execute(plan);
d@0 67 fftw_destroy_plan(plan);
d@0 68 </pre>
d@0 69 <p>In Fortran, you would use the following to accomplish the same thing:
d@0 70
d@0 71 <pre class="example"> double complex in, out
d@0 72 dimension in(N), out(N)
d@0 73 integer*8 plan
d@0 74
d@0 75 call dfftw_plan_dft_1d(plan,N,in,out,FFTW_FORWARD,FFTW_ESTIMATE)
d@0 76 call dfftw_execute_dft(plan, in, out)
d@0 77 call dfftw_destroy_plan(plan)
d@0 78 </pre>
d@0 79 <p><a name="index-dfftw_005fplan_005fdft_005f1d-341"></a><a name="index-dfftw_005fexecute_005fdft-342"></a><a name="index-dfftw_005fdestroy_005fplan-343"></a>
d@0 80 Notice how all routines are called as Fortran subroutines, and the
d@0 81 plan is returned via the first argument to <code>dfftw_plan_dft_1d</code>.
d@0 82 Notice also that we changed <code>fftw_execute</code> to
d@0 83 <code>dfftw_execute_dft</code> (see <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>). To do
d@0 84 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:
d@0 85
d@0 86 <pre class="example"> call dfftw_init_threads
d@0 87 call dfftw_plan_with_nthreads(8)
d@0 88 </pre>
d@0 89 <p><a name="index-dfftw_005finit_005fthreads-344"></a><a name="index-dfftw_005fplan_005fwith_005fnthreads-345"></a>
d@0 90 To transform a three-dimensional array in-place with C, you might do:
d@0 91
d@0 92 <pre class="example"> fftw_complex arr[L][M][N];
d@0 93 fftw_plan plan;
d@0 94
d@0 95 plan = fftw_plan_dft_3d(L,M,N, arr,arr,
d@0 96 FFTW_FORWARD, FFTW_ESTIMATE);
d@0 97 fftw_execute(plan);
d@0 98 fftw_destroy_plan(plan);
d@0 99 </pre>
d@0 100 <p>In Fortran, you would use this instead:
d@0 101
d@0 102 <pre class="example"> double complex arr
d@0 103 dimension arr(L,M,N)
d@0 104 integer*8 plan
d@0 105
d@0 106 call dfftw_plan_dft_3d(plan, L,M,N, arr,arr,
d@0 107 &amp; FFTW_FORWARD, FFTW_ESTIMATE)
d@0 108 call dfftw_execute_dft(plan, arr, arr)
d@0 109 call dfftw_destroy_plan(plan)
d@0 110 </pre>
d@0 111 <p><a name="index-dfftw_005fplan_005fdft_005f3d-346"></a>
d@0 112 Note that we pass the array dimensions in the &ldquo;natural&rdquo; order in both C
d@0 113 and Fortran.
d@0 114
d@0 115 <p>To transform a one-dimensional real array in Fortran, you might do:
d@0 116
d@0 117 <pre class="example"> double precision in
d@0 118 dimension in(N)
d@0 119 double complex out
d@0 120 dimension out(N/2 + 1)
d@0 121 integer*8 plan
d@0 122
d@0 123 call dfftw_plan_dft_r2c_1d(plan,N,in,out,FFTW_ESTIMATE)
d@0 124 call dfftw_execute_dft_r2c(plan, in, out)
d@0 125 call dfftw_destroy_plan(plan)
d@0 126 </pre>
d@0 127 <p><a name="index-dfftw_005fplan_005fdft_005fr2c_005f1d-347"></a><a name="index-dfftw_005fexecute_005fdft_005fr2c-348"></a>
d@0 128 To transform a two-dimensional real array, out of place, you might use
d@0 129 the following:
d@0 130
d@0 131 <pre class="example"> double precision in
d@0 132 dimension in(M,N)
d@0 133 double complex out
d@0 134 dimension out(M/2 + 1, N)
d@0 135 integer*8 plan
d@0 136
d@0 137 call dfftw_plan_dft_r2c_2d(plan,M,N,in,out,FFTW_ESTIMATE)
d@0 138 call dfftw_execute_dft_r2c(plan, in, out)
d@0 139 call dfftw_destroy_plan(plan)
d@0 140 </pre>
d@0 141 <p><a name="index-dfftw_005fplan_005fdft_005fr2c_005f2d-349"></a>
d@0 142 <strong>Important:</strong> Notice that it is the <em>first</em> dimension of the
d@0 143 complex output array that is cut in half in Fortran, rather than the
d@0 144 last dimension as in C. This is a consequence of the interface routines
d@0 145 reversing the order of the array dimensions passed to FFTW so that the
d@0 146 Fortran program can use its ordinary column-major order.
d@0 147 <a name="index-column_002dmajor-350"></a><a name="index-r2c_002fc2r-multi_002ddimensional-array-format-351"></a>
d@0 148 <!-- -->
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d@0 151