Mercurial > hg > sv-dependency-builds

comparison src/fftw-3.3.5/doc/html/Overview-of-Fortran-interface.html @ 42:2cd0e3b3e1fd

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Current fftw source
author Chris Cannam
date Tue, 18 Oct 2016 13:40:26 +0100
parents
children
comparison
equal deleted inserted replaced
41:481f5f8c5634 42:2cd0e3b3e1fd
1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
2 <html>
3 <!-- This manual is for FFTW
4 (version 3.3.5, 30 July 2016).
5
6 Copyright (C) 2003 Matteo Frigo.
7
8 Copyright (C) 2003 Massachusetts Institute of Technology.
9
10 Permission is granted to make and distribute verbatim copies of this
11 manual provided the copyright notice and this permission notice are
12 preserved on all copies.
13
14 Permission is granted to copy and distribute modified versions of this
15 manual under the conditions for verbatim copying, provided that the
16 entire resulting derived work is distributed under the terms of a
17 permission notice identical to this one.
18
19 Permission is granted to copy and distribute translations of this manual
20 into another language, under the above conditions for modified versions,
21 except that this permission notice may be stated in a translation
22 approved by the Free Software Foundation. -->
23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
24 <head>
25 <title>FFTW 3.3.5: Overview of Fortran interface</title>
26
27 <meta name="description" content="FFTW 3.3.5: Overview of Fortran interface">
28 <meta name="keywords" content="FFTW 3.3.5: Overview of Fortran interface">
29 <meta name="resource-type" content="document">
30 <meta name="distribution" content="global">
31 <meta name="Generator" content="makeinfo">
32 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
33 <link href="index.html#Top" rel="start" title="Top">
34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
36 <link href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" rel="up" title="Calling FFTW from Modern Fortran">
37 <link href="Extended-and-quadruple-precision-in-Fortran.html#Extended-and-quadruple-precision-in-Fortran" rel="next" title="Extended and quadruple precision in Fortran">
38 <link href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" rel="prev" title="Calling FFTW from Modern Fortran">
39 <style type="text/css">
40 <!--
41 a.summary-letter {text-decoration: none}
42 blockquote.smallquotation {font-size: smaller}
43 div.display {margin-left: 3.2em}
44 div.example {margin-left: 3.2em}
45 div.indentedblock {margin-left: 3.2em}
46 div.lisp {margin-left: 3.2em}
47 div.smalldisplay {margin-left: 3.2em}
48 div.smallexample {margin-left: 3.2em}
49 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
50 div.smalllisp {margin-left: 3.2em}
51 kbd {font-style:oblique}
52 pre.display {font-family: inherit}
53 pre.format {font-family: inherit}
54 pre.menu-comment {font-family: serif}
55 pre.menu-preformatted {font-family: serif}
56 pre.smalldisplay {font-family: inherit; font-size: smaller}
57 pre.smallexample {font-size: smaller}
58 pre.smallformat {font-family: inherit; font-size: smaller}
59 pre.smalllisp {font-size: smaller}
60 span.nocodebreak {white-space:nowrap}
61 span.nolinebreak {white-space:nowrap}
62 span.roman {font-family:serif; font-weight:normal}
63 span.sansserif {font-family:sans-serif; font-weight:normal}
64 ul.no-bullet {list-style: none}
65 -->
66 </style>
67
68
69 </head>
70
71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
72 <a name="Overview-of-Fortran-interface"></a>
73 <div class="header">
74 <p>
75 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> &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>
76 </div>
77 <hr>
78 <a name="Overview-of-Fortran-interface-1"></a>
79 <h3 class="section">7.1 Overview of Fortran interface</h3>
80
81 <p>FFTW provides a file <code>fftw3.f03</code> that defines Fortran 2003
82 interfaces for all of its C routines, except for the MPI routines
83 described elsewhere, which can be found in the same directory as
84 <code>fftw3.h</code> (the C header file). In any Fortran subroutine where
85 you want to use FFTW functions, you should begin with:
86 </p>
87 <a name="index-iso_005fc_005fbinding-1"></a>
88 <div class="example">
89 <pre class="example"> use, intrinsic :: iso_c_binding
90 include 'fftw3.f03'
91 </pre></div>
92
93 <p>This includes the interface definitions and the standard
94 <code>iso_c_binding</code> module (which defines the equivalents of C
95 types). You can also put the FFTW functions into a module if you
96 prefer (see <a href="Defining-an-FFTW-module.html#Defining-an-FFTW-module">Defining an FFTW module</a>).
97 </p>
98 <p>At this point, you can now call anything in the FFTW C interface
99 directly, almost exactly as in C other than minor changes in syntax.
100 For example:
101 </p>
102 <a name="index-fftw_005fplan_005fdft_005f2d-2"></a>
103 <a name="index-fftw_005fexecute_005fdft-2"></a>
104 <a name="index-fftw_005fdestroy_005fplan-3"></a>
105 <div class="example">
106 <pre class="example"> type(C_PTR) :: plan
107 complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out
108 plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE)
109 ...
110 call fftw_execute_dft(plan, in, out)
111 ...
112 call fftw_destroy_plan(plan)
113 </pre></div>
114
115 <p>A few important things to keep in mind are:
116 </p>
117 <ul>
118 <li> <a name="index-fftw_005fcomplex-2"></a>
119 <a name="index-C_005fPTR"></a>
120 <a name="index-C_005fINT"></a>
121 <a name="index-C_005fDOUBLE"></a>
122 <a name="index-C_005fDOUBLE_005fCOMPLEX"></a>
123 FFTW plans are <code>type(C_PTR)</code>. Other C types are mapped in the
124 obvious way via the <code>iso_c_binding</code> standard: <code>int</code> turns
125 into <code>integer(C_INT)</code>, <code>fftw_complex</code> turns into
126 <code>complex(C_DOUBLE_COMPLEX)</code>, <code>double</code> turns into
127 <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>.
128
129 </li><li> Functions in C become functions in Fortran if they have a return value,
130 and subroutines in Fortran otherwise.
131
132 </li><li> The ordering of the Fortran array dimensions must be <em>reversed</em>
133 when they are passed to the FFTW plan creation, thanks to differences
134 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
135 (see <a href="Fortran_002dinterface-routines.html#Fortran_002dinterface-routines">Fortran-interface routines</a>), which reversed the dimensions
136 for you. See <a href="Reversing-array-dimensions.html#Reversing-array-dimensions">Reversing array dimensions</a>.
137
138 </li><li> <a name="index-alignment-4"></a>
139 <a name="index-SIMD-2"></a>
140 Using ordinary Fortran array declarations like this works, but may
141 yield suboptimal performance because the data may not be not aligned
142 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
143 by allocating with &lsquo;<samp>fftw_alloc</samp>&rsquo;. See <a href="Allocating-aligned-memory-in-Fortran.html#Allocating-aligned-memory-in-Fortran">Allocating aligned memory in Fortran</a>.
144
145 </li><li> <a name="index-fftw_005fexecute-5"></a>
146 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>
147 but rather using the more specialized functions like
148 <code>fftw_execute_dft</code> (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>).
149 However, you should execute the plan on the <code>same arrays</code> as the
150 ones for which you created the plan, unless you are especially
151 careful. See <a href="Plan-execution-in-Fortran.html#Plan-execution-in-Fortran">Plan execution in Fortran</a>. To prevent
152 you from using <code>fftw_execute</code> by mistake, the <code>fftw3.f03</code>
153 file does not provide an <code>fftw_execute</code> interface declaration.
154
155 </li><li> <a name="index-flags-8"></a>
156 Multiple planner flags are combined with <code>ior</code> (equivalent to &lsquo;<samp>|</samp>&rsquo; in C). e.g. <code>FFTW_MEASURE | FFTW_DESTROY_INPUT</code> becomes <code>ior(FFTW_MEASURE, FFTW_DESTROY_INPUT)</code>. (You can also use &lsquo;<samp>+</samp>&rsquo; as long as you don&rsquo;t try to include a given flag more than once.)
157
158 </li></ul>
159
160 <table class="menu" border="0" cellspacing="0">
161 <tr><td align="left" valign="top">&bull; <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>&nbsp;&nbsp;</td><td align="left" valign="top">
162 </td></tr>
163 </table>
164
165 <hr>
166 <div class="header">
167 <p>
168 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> &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>
169 </div>
170
171
172
173 </body>
174 </html>