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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<!-- This manual is for FFTW
+(version 3.3.8, 24 May 2018).
+
+Copyright (C) 2003 Matteo Frigo.
+
+Copyright (C) 2003 Massachusetts Institute of Technology.
+
+Permission is granted to make and distribute verbatim copies of this
+manual provided the copyright notice and this permission notice are
+preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the
+entire resulting derived work is distributed under the terms of a
+permission notice identical to this one.
+
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+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation
+approved by the Free Software Foundation. -->
+<!-- Created by GNU Texinfo 6.3, http://www.gnu.org/software/texinfo/ -->
+<head>
+<title>FFTW 3.3.8: Fortran Examples</title>
+
+<meta name="description" content="FFTW 3.3.8: Fortran Examples">
+<meta name="keywords" content="FFTW 3.3.8: Fortran Examples">
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+<link href="index.html#Top" rel="start" title="Top">
+<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
+<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
+<link href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" rel="up" title="Calling FFTW from Legacy Fortran">
+<link href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f" rel="next" title="Wisdom of Fortran?">
+<link href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran" rel="prev" title="FFTW Execution in Fortran">
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+</head>
+
+<body lang="en">
+<a name="Fortran-Examples"></a>
+<div class="header">
+<p>
+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>
+</div>
+<hr>
+<a name="Fortran-Examples-1"></a>
+<h3 class="section">8.4 Fortran Examples</h3>
+
+<p>In C, you might have something like the following to transform a
+one-dimensional complex array:
+</p>
+<div class="example">
+<pre class="example">        fftw_complex in[N], out[N];
+        fftw_plan plan;
+
+        plan = fftw_plan_dft_1d(N,in,out,FFTW_FORWARD,FFTW_ESTIMATE);
+        fftw_execute(plan);
+        fftw_destroy_plan(plan);
+</pre></div>
+
+<p>In Fortran, you would use the following to accomplish the same thing:
+</p>
+<div class="example">
+<pre class="example">        double complex in, out
+        dimension in(N), out(N)
+        integer*8 plan
+
+        call dfftw_plan_dft_1d(plan,N,in,out,FFTW_FORWARD,FFTW_ESTIMATE)
+        call dfftw_execute_dft(plan, in, out)
+        call dfftw_destroy_plan(plan)
+</pre></div>
+<a name="index-dfftw_005fplan_005fdft_005f1d"></a>
+<a name="index-dfftw_005fexecute_005fdft-1"></a>
+<a name="index-dfftw_005fdestroy_005fplan"></a>
+
+<p>Notice how all routines are called as Fortran subroutines, and the
+plan is returned via the first argument to <code>dfftw_plan_dft_1d</code>.
+Notice also that we changed <code>fftw_execute</code> to
+<code>dfftw_execute_dft</code> (see <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>).  To do
+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:
+</p>
+<div class="example">
+<pre class="example">        integer iret
+        call dfftw_init_threads(iret)
+        call dfftw_plan_with_nthreads(8)
+</pre></div>
+<a name="index-dfftw_005finit_005fthreads"></a>
+<a name="index-dfftw_005fplan_005fwith_005fnthreads"></a>
+
+<p>(You might want to check the value of <code>iret</code>: if it is zero, it
+indicates an unlikely error during thread initialization.)
+</p>
+<p>To transform a three-dimensional array in-place with C, you might do:
+</p>
+<div class="example">
+<pre class="example">        fftw_complex arr[L][M][N];
+        fftw_plan plan;
+
+        plan = fftw_plan_dft_3d(L,M,N, arr,arr,
+                                FFTW_FORWARD, FFTW_ESTIMATE);
+        fftw_execute(plan);
+        fftw_destroy_plan(plan);
+</pre></div>
+
+<p>In Fortran, you would use this instead:
+</p>
+<div class="example">
+<pre class="example">        double complex arr
+        dimension arr(L,M,N)
+        integer*8 plan
+
+        call dfftw_plan_dft_3d(plan, L,M,N, arr,arr,
+       &amp;                       FFTW_FORWARD, FFTW_ESTIMATE)
+        call dfftw_execute_dft(plan, arr, arr)
+        call dfftw_destroy_plan(plan)
+</pre></div>
+<a name="index-dfftw_005fplan_005fdft_005f3d"></a>
+
+<p>Note that we pass the array dimensions in the &ldquo;natural&rdquo; order in both C
+and Fortran.
+</p>
+<p>To transform a one-dimensional real array in Fortran, you might do:
+</p>
+<div class="example">
+<pre class="example">        double precision in
+        dimension in(N)
+        double complex out
+        dimension out(N/2 + 1)
+        integer*8 plan
+
+        call dfftw_plan_dft_r2c_1d(plan,N,in,out,FFTW_ESTIMATE)
+        call dfftw_execute_dft_r2c(plan, in, out)
+        call dfftw_destroy_plan(plan)
+</pre></div>
+<a name="index-dfftw_005fplan_005fdft_005fr2c_005f1d"></a>
+<a name="index-dfftw_005fexecute_005fdft_005fr2c"></a>
+
+<p>To transform a two-dimensional real array, out of place, you might use
+the following:
+</p>
+<div class="example">
+<pre class="example">        double precision in
+        dimension in(M,N)
+        double complex out
+        dimension out(M/2 + 1, N)
+        integer*8 plan
+
+        call dfftw_plan_dft_r2c_2d(plan,M,N,in,out,FFTW_ESTIMATE)
+        call dfftw_execute_dft_r2c(plan, in, out)
+        call dfftw_destroy_plan(plan)
+</pre></div>
+<a name="index-dfftw_005fplan_005fdft_005fr2c_005f2d"></a>
+
+<p><strong>Important:</strong> Notice that it is the <em>first</em> dimension of the
+complex output array that is cut in half in Fortran, rather than the
+last dimension as in C.  This is a consequence of the interface routines
+reversing the order of the array dimensions passed to FFTW so that the
+Fortran program can use its ordinary column-major order.
+<a name="index-column_002dmajor-3"></a>
+<a name="index-r2c_002fc2r-multi_002ddimensional-array-format-3"></a>
+</p>
+<hr>
+<div class="header">
+<p>
+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>
+</div>
+
+
+
+</body>
+</html>