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diff src/fftw-3.3.3/doc/html/Fortran-Examples.html @ 10:37bf6b4a2645
Add FFTW3
| author | Chris Cannam |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Fortran-Examples.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,155 @@ +<html lang="en"> +<head> +<title>Fortran Examples - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" title="Calling FFTW from Legacy Fortran"> +<link rel="prev" href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran" title="FFTW Execution in Fortran"> +<link rel="next" href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f" title="Wisdom of Fortran?"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +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. + + Permission is granted to copy and distribute translations of this + manual 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. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="Fortran-Examples"></a> +<p> +Next: <a rel="next" accesskey="n" href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f">Wisdom of Fortran?</a>, +Previous: <a rel="previous" accesskey="p" href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>, +Up: <a rel="up" accesskey="u" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran">Calling FFTW from Legacy Fortran</a> +<hr> +</div> + +<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: + +<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> + <p>In Fortran, you would use the following to accomplish the same thing: + +<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> + <p><a name="index-dfftw_005fplan_005fdft_005f1d-587"></a><a name="index-dfftw_005fexecute_005fdft-588"></a><a name="index-dfftw_005fdestroy_005fplan-589"></a> +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: + +<pre class="example"> integer iret + call dfftw_init_threads(iret) + call dfftw_plan_with_nthreads(8) +</pre> + <p><a name="index-dfftw_005finit_005fthreads-590"></a><a name="index-dfftw_005fplan_005fwith_005fnthreads-591"></a> +(You might want to check the value of <code>iret</code>: if it is zero, it +indicates an unlikely error during thread initialization.) + + <p>To transform a three-dimensional array in-place with C, you might do: + +<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> + <p>In Fortran, you would use this instead: + +<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, + & FFTW_FORWARD, FFTW_ESTIMATE) + call dfftw_execute_dft(plan, arr, arr) + call dfftw_destroy_plan(plan) +</pre> + <p><a name="index-dfftw_005fplan_005fdft_005f3d-592"></a> +Note that we pass the array dimensions in the “natural” order in both C +and Fortran. + + <p>To transform a one-dimensional real array in Fortran, you might do: + +<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> + <p><a name="index-dfftw_005fplan_005fdft_005fr2c_005f1d-593"></a><a name="index-dfftw_005fexecute_005fdft_005fr2c-594"></a> +To transform a two-dimensional real array, out of place, you might use +the following: + +<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> + <p><a name="index-dfftw_005fplan_005fdft_005fr2c_005f2d-595"></a> +<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-596"></a><a name="index-r2c_002fc2r-multi_002ddimensional-array-format-597"></a> +<!-- --> + + </body></html> +