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| author | Chris Cannam <cannam@all-day-breakfast.com> |
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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/Overview-of-Fortran-interface.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,128 @@ +<html lang="en"> +<head> +<title>Overview of Fortran interface - 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-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" title="Calling FFTW from Modern Fortran"> +<link rel="prev" href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" title="Calling FFTW from Modern Fortran"> +<link rel="next" href="Reversing-array-dimensions.html#Reversing-array-dimensions" title="Reversing array dimensions"> +<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="Overview-of-Fortran-interface"></a> +<p> +Next: <a rel="next" accesskey="n" href="Reversing-array-dimensions.html#Reversing-array-dimensions">Reversing array dimensions</a>, +Previous: <a rel="previous" accesskey="p" href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran">Calling FFTW from Modern Fortran</a>, +Up: <a rel="up" accesskey="u" href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran">Calling FFTW from Modern Fortran</a> +<hr> +</div> + +<h3 class="section">7.1 Overview of Fortran interface</h3> + +<p>FFTW provides a file <code>fftw3.f03</code> that defines Fortran 2003 +interfaces for all of its C routines, except for the MPI routines +described elsewhere, which can be found in the same directory as +<code>fftw3.h</code> (the C header file). In any Fortran subroutine where +you want to use FFTW functions, you should begin with: + + <p><a name="index-iso_005fc_005fbinding-502"></a> +<pre class="example"> use, intrinsic :: iso_c_binding + include 'fftw3.f03' +</pre> + <p>This includes the interface definitions and the standard +<code>iso_c_binding</code> module (which defines the equivalents of C +types). You can also put the FFTW functions into a module if you +prefer (see <a href="Defining-an-FFTW-module.html#Defining-an-FFTW-module">Defining an FFTW module</a>). + + <p>At this point, you can now call anything in the FFTW C interface +directly, almost exactly as in C other than minor changes in syntax. +For example: + + <p><a name="index-fftw_005fplan_005fdft_005f2d-503"></a><a name="index-fftw_005fexecute_005fdft-504"></a><a name="index-fftw_005fdestroy_005fplan-505"></a> +<pre class="example"> type(C_PTR) :: plan + complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out + plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE) + ... + call fftw_execute_dft(plan, in, out) + ... + call fftw_destroy_plan(plan) +</pre> + <p>A few important things to keep in mind are: + + <ul> +<li><a name="index-fftw_005fcomplex-506"></a><a name="index-C_005fPTR-507"></a><a name="index-C_005fINT-508"></a><a name="index-C_005fDOUBLE-509"></a><a name="index-C_005fDOUBLE_005fCOMPLEX-510"></a>FFTW plans are <code>type(C_PTR)</code>. Other C types are mapped in the +obvious way via the <code>iso_c_binding</code> standard: <code>int</code> turns +into <code>integer(C_INT)</code>, <code>fftw_complex</code> turns into +<code>complex(C_DOUBLE_COMPLEX)</code>, <code>double</code> turns into +<code>real(C_DOUBLE)</code>, and so on. See <a href="FFTW-Fortran-type-reference.html#FFTW-Fortran-type-reference">FFTW Fortran type reference</a>. + + <li>Functions in C become functions in Fortran if they have a return value, +and subroutines in Fortran otherwise. + + <li>The ordering of the Fortran array dimensions must be <em>reversed</em> +when they are passed to the FFTW plan creation, thanks to differences +in array indexing conventions (see <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>). This is <em>unlike</em> the legacy Fortran interface +(see <a href="Fortran_002dinterface-routines.html#Fortran_002dinterface-routines">Fortran-interface routines</a>), which reversed the dimensions +for you. See <a href="Reversing-array-dimensions.html#Reversing-array-dimensions">Reversing array dimensions</a>. + + <li><a name="index-alignment-511"></a><a name="index-SIMD-512"></a>Using ordinary Fortran array declarations like this works, but may +yield suboptimal performance because the data may not be not aligned +to exploit SIMD instructions on modern proessors (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>). Better performance will often be obtained +by allocating with ‘<samp><span class="samp">fftw_alloc</span></samp>’. See <a href="Allocating-aligned-memory-in-Fortran.html#Allocating-aligned-memory-in-Fortran">Allocating aligned memory in Fortran</a>. + + <li><a name="index-fftw_005fexecute-513"></a>Similar to the legacy Fortran interface (see <a href="FFTW-Execution-in-Fortran.html#FFTW-Execution-in-Fortran">FFTW Execution in Fortran</a>), we currently recommend <em>not</em> using <code>fftw_execute</code> +but rather using the more specialized functions like +<code>fftw_execute_dft</code> (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>). +However, you should execute the plan on the <code>same arrays</code> as the +ones for which you created the plan, unless you are especially +careful. See <a href="Plan-execution-in-Fortran.html#Plan-execution-in-Fortran">Plan execution in Fortran</a>. To prevent +you from using <code>fftw_execute</code> by mistake, the <code>fftw3.f03</code> +file does not provide an <code>fftw_execute</code> interface declaration. + + <li><a name="index-flags-514"></a>Multiple planner flags are combined with <code>ior</code> (equivalent to ‘<samp><span class="samp">|</span></samp>’ in C). e.g. <code>FFTW_MEASURE | FFTW_DESTROY_INPUT</code> becomes <code>ior(FFTW_MEASURE, FFTW_DESTROY_INPUT)</code>. (You can also use ‘<samp><span class="samp">+</span></samp>’ as long as you don't try to include a given flag more than once.) + + </ul> + +<ul class="menu"> +<li><a accesskey="1" href="Extended-and-quadruple-precision-in-Fortran.html#Extended-and-quadruple-precision-in-Fortran">Extended and quadruple precision in Fortran</a> +</ul> + + </body></html> +