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Add null config files
author Chris Cannam <cannam@all-day-breakfast.com>
date Mon, 02 Mar 2020 14:03:47 +0000
parents 7867fa7e1b6b
children
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cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
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cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: Overview of Fortran interface</title>
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cannam@127 69 </head>
cannam@127 70
cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="Overview-of-Fortran-interface"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="Overview-of-Fortran-interface-1"></a>
cannam@127 79 <h3 class="section">7.1 Overview of Fortran interface</h3>
cannam@127 80
cannam@127 81 <p>FFTW provides a file <code>fftw3.f03</code> that defines Fortran 2003
cannam@127 82 interfaces for all of its C routines, except for the MPI routines
cannam@127 83 described elsewhere, which can be found in the same directory as
cannam@127 84 <code>fftw3.h</code> (the C header file). In any Fortran subroutine where
cannam@127 85 you want to use FFTW functions, you should begin with:
cannam@127 86 </p>
cannam@127 87 <a name="index-iso_005fc_005fbinding-1"></a>
cannam@127 88 <div class="example">
cannam@127 89 <pre class="example"> use, intrinsic :: iso_c_binding
cannam@127 90 include 'fftw3.f03'
cannam@127 91 </pre></div>
cannam@127 92
cannam@127 93 <p>This includes the interface definitions and the standard
cannam@127 94 <code>iso_c_binding</code> module (which defines the equivalents of C
cannam@127 95 types). You can also put the FFTW functions into a module if you
cannam@127 96 prefer (see <a href="Defining-an-FFTW-module.html#Defining-an-FFTW-module">Defining an FFTW module</a>).
cannam@127 97 </p>
cannam@127 98 <p>At this point, you can now call anything in the FFTW C interface
cannam@127 99 directly, almost exactly as in C other than minor changes in syntax.
cannam@127 100 For example:
cannam@127 101 </p>
cannam@127 102 <a name="index-fftw_005fplan_005fdft_005f2d-2"></a>
cannam@127 103 <a name="index-fftw_005fexecute_005fdft-2"></a>
cannam@127 104 <a name="index-fftw_005fdestroy_005fplan-3"></a>
cannam@127 105 <div class="example">
cannam@127 106 <pre class="example"> type(C_PTR) :: plan
cannam@127 107 complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out
cannam@127 108 plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE)
cannam@127 109 ...
cannam@127 110 call fftw_execute_dft(plan, in, out)
cannam@127 111 ...
cannam@127 112 call fftw_destroy_plan(plan)
cannam@127 113 </pre></div>
cannam@127 114
cannam@127 115 <p>A few important things to keep in mind are:
cannam@127 116 </p>
cannam@127 117 <ul>
cannam@127 118 <li> <a name="index-fftw_005fcomplex-2"></a>
cannam@127 119 <a name="index-C_005fPTR"></a>
cannam@127 120 <a name="index-C_005fINT"></a>
cannam@127 121 <a name="index-C_005fDOUBLE"></a>
cannam@127 122 <a name="index-C_005fDOUBLE_005fCOMPLEX"></a>
cannam@127 123 FFTW plans are <code>type(C_PTR)</code>. Other C types are mapped in the
cannam@127 124 obvious way via the <code>iso_c_binding</code> standard: <code>int</code> turns
cannam@127 125 into <code>integer(C_INT)</code>, <code>fftw_complex</code> turns into
cannam@127 126 <code>complex(C_DOUBLE_COMPLEX)</code>, <code>double</code> turns into
cannam@127 127 <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>.
cannam@127 128
cannam@127 129 </li><li> Functions in C become functions in Fortran if they have a return value,
cannam@127 130 and subroutines in Fortran otherwise.
cannam@127 131
cannam@127 132 </li><li> The ordering of the Fortran array dimensions must be <em>reversed</em>
cannam@127 133 when they are passed to the FFTW plan creation, thanks to differences
cannam@127 134 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
cannam@127 135 (see <a href="Fortran_002dinterface-routines.html#Fortran_002dinterface-routines">Fortran-interface routines</a>), which reversed the dimensions
cannam@127 136 for you. See <a href="Reversing-array-dimensions.html#Reversing-array-dimensions">Reversing array dimensions</a>.
cannam@127 137
cannam@127 138 </li><li> <a name="index-alignment-4"></a>
cannam@127 139 <a name="index-SIMD-2"></a>
cannam@127 140 Using ordinary Fortran array declarations like this works, but may
cannam@127 141 yield suboptimal performance because the data may not be not aligned
cannam@127 142 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
cannam@127 143 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>.
cannam@127 144
cannam@127 145 </li><li> <a name="index-fftw_005fexecute-5"></a>
cannam@127 146 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>
cannam@127 147 but rather using the more specialized functions like
cannam@127 148 <code>fftw_execute_dft</code> (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>).
cannam@127 149 However, you should execute the plan on the <code>same arrays</code> as the
cannam@127 150 ones for which you created the plan, unless you are especially
cannam@127 151 careful. See <a href="Plan-execution-in-Fortran.html#Plan-execution-in-Fortran">Plan execution in Fortran</a>. To prevent
cannam@127 152 you from using <code>fftw_execute</code> by mistake, the <code>fftw3.f03</code>
cannam@127 153 file does not provide an <code>fftw_execute</code> interface declaration.
cannam@127 154
cannam@127 155 </li><li> <a name="index-flags-8"></a>
cannam@127 156 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.)
cannam@127 157
cannam@127 158 </li></ul>
cannam@127 159
cannam@127 160 <table class="menu" border="0" cellspacing="0">
cannam@127 161 <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">
cannam@127 162 </td></tr>
cannam@127 163 </table>
cannam@127 164
cannam@127 165 <hr>
cannam@127 166 <div class="header">
cannam@127 167 <p>
cannam@127 168 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>
cannam@127 169 </div>
cannam@127 170
cannam@127 171
cannam@127 172
cannam@127 173 </body>
cannam@127 174 </html>