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Current fftw source
| author | Chris Cannam <cannam@all-day-breakfast.com> |
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| date | Tue, 18 Oct 2016 13:40:26 +0100 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.5/doc/html/Overview-of-Fortran-interface.html Tue Oct 18 13:40:26 2016 +0100 @@ -0,0 +1,174 @@ +<!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 3.3.5, 30 July 2016). + +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. --> +<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> +<head> +<title>FFTW 3.3.5: Overview of Fortran interface</title> + +<meta name="description" content="FFTW 3.3.5: Overview of Fortran interface"> +<meta name="keywords" content="FFTW 3.3.5: Overview of Fortran interface"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<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-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" rel="up" title="Calling FFTW from Modern Fortran"> +<link href="Extended-and-quadruple-precision-in-Fortran.html#Extended-and-quadruple-precision-in-Fortran" rel="next" title="Extended and quadruple precision in Fortran"> +<link href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" rel="prev" title="Calling FFTW from Modern Fortran"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Overview-of-Fortran-interface"></a> +<div class="header"> +<p> +Next: <a href="Reversing-array-dimensions.html#Reversing-array-dimensions" accesskey="n" rel="next">Reversing array dimensions</a>, Previous: <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" accesskey="p" rel="prev">Calling FFTW from Modern Fortran</a>, Up: <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" accesskey="u" rel="up">Calling FFTW from Modern Fortran</a> [<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="Overview-of-Fortran-interface-1"></a> +<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-1"></a> +<div class="example"> +<pre class="example"> use, intrinsic :: iso_c_binding + include 'fftw3.f03' +</pre></div> + +<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> +<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-2"></a> +<a name="index-fftw_005fexecute_005fdft-2"></a> +<a name="index-fftw_005fdestroy_005fplan-3"></a> +<div class="example"> +<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></div> + +<p>A few important things to keep in mind are: +</p> +<ul> +<li> <a name="index-fftw_005fcomplex-2"></a> +<a name="index-C_005fPTR"></a> +<a name="index-C_005fINT"></a> +<a name="index-C_005fDOUBLE"></a> +<a name="index-C_005fDOUBLE_005fCOMPLEX"></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><li> Functions in C become functions in Fortran if they have a return value, +and subroutines in Fortran otherwise. + +</li><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><li> <a name="index-alignment-4"></a> +<a name="index-SIMD-2"></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>fftw_alloc</samp>’. See <a href="Allocating-aligned-memory-in-Fortran.html#Allocating-aligned-memory-in-Fortran">Allocating aligned memory in Fortran</a>. + +</li><li> <a name="index-fftw_005fexecute-5"></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><li> <a name="index-flags-8"></a> +Multiple planner flags are combined with <code>ior</code> (equivalent to ‘<samp>|</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>+</samp>’ as long as you don’t try to include a given flag more than once.) + +</li></ul> + +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="Extended-and-quadruple-precision-in-Fortran.html#Extended-and-quadruple-precision-in-Fortran" accesskey="1">Extended and quadruple precision in Fortran</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +</table> + +<hr> +<div class="header"> +<p> +Next: <a href="Reversing-array-dimensions.html#Reversing-array-dimensions" accesskey="n" rel="next">Reversing array dimensions</a>, Previous: <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" accesskey="p" rel="prev">Calling FFTW from Modern Fortran</a>, Up: <a href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" accesskey="u" rel="up">Calling FFTW from Modern Fortran</a> [<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>