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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 bd3cc4d1df30
children
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cannam@167 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
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cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: Overview of Fortran interface</title>
cannam@167 26
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cannam@167 36 <link href="Calling-FFTW-from-Modern-Fortran.html#Calling-FFTW-from-Modern-Fortran" rel="up" title="Calling FFTW from Modern Fortran">
cannam@167 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">
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cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="Overview-of-Fortran-interface"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 74 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@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="Overview-of-Fortran-interface-1"></a>
cannam@167 78 <h3 class="section">7.1 Overview of Fortran interface</h3>
cannam@167 79
cannam@167 80 <p>FFTW provides a file <code>fftw3.f03</code> that defines Fortran 2003
cannam@167 81 interfaces for all of its C routines, except for the MPI routines
cannam@167 82 described elsewhere, which can be found in the same directory as
cannam@167 83 <code>fftw3.h</code> (the C header file). In any Fortran subroutine where
cannam@167 84 you want to use FFTW functions, you should begin with:
cannam@167 85 </p>
cannam@167 86 <a name="index-iso_005fc_005fbinding-1"></a>
cannam@167 87 <div class="example">
cannam@167 88 <pre class="example"> use, intrinsic :: iso_c_binding
cannam@167 89 include 'fftw3.f03'
cannam@167 90 </pre></div>
cannam@167 91
cannam@167 92 <p>This includes the interface definitions and the standard
cannam@167 93 <code>iso_c_binding</code> module (which defines the equivalents of C
cannam@167 94 types). You can also put the FFTW functions into a module if you
cannam@167 95 prefer (see <a href="Defining-an-FFTW-module.html#Defining-an-FFTW-module">Defining an FFTW module</a>).
cannam@167 96 </p>
cannam@167 97 <p>At this point, you can now call anything in the FFTW C interface
cannam@167 98 directly, almost exactly as in C other than minor changes in syntax.
cannam@167 99 For example:
cannam@167 100 </p>
cannam@167 101 <a name="index-fftw_005fplan_005fdft_005f2d-2"></a>
cannam@167 102 <a name="index-fftw_005fexecute_005fdft-2"></a>
cannam@167 103 <a name="index-fftw_005fdestroy_005fplan-3"></a>
cannam@167 104 <div class="example">
cannam@167 105 <pre class="example"> type(C_PTR) :: plan
cannam@167 106 complex(C_DOUBLE_COMPLEX), dimension(1024,1000) :: in, out
cannam@167 107 plan = fftw_plan_dft_2d(1000,1024, in,out, FFTW_FORWARD,FFTW_ESTIMATE)
cannam@167 108 ...
cannam@167 109 call fftw_execute_dft(plan, in, out)
cannam@167 110 ...
cannam@167 111 call fftw_destroy_plan(plan)
cannam@167 112 </pre></div>
cannam@167 113
cannam@167 114 <p>A few important things to keep in mind are:
cannam@167 115 </p>
cannam@167 116 <ul>
cannam@167 117 <li> <a name="index-fftw_005fcomplex-2"></a>
cannam@167 118 <a name="index-C_005fPTR"></a>
cannam@167 119 <a name="index-C_005fINT"></a>
cannam@167 120 <a name="index-C_005fDOUBLE"></a>
cannam@167 121 <a name="index-C_005fDOUBLE_005fCOMPLEX"></a>
cannam@167 122 FFTW plans are <code>type(C_PTR)</code>. Other C types are mapped in the
cannam@167 123 obvious way via the <code>iso_c_binding</code> standard: <code>int</code> turns
cannam@167 124 into <code>integer(C_INT)</code>, <code>fftw_complex</code> turns into
cannam@167 125 <code>complex(C_DOUBLE_COMPLEX)</code>, <code>double</code> turns into
cannam@167 126 <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@167 127
cannam@167 128 </li><li> Functions in C become functions in Fortran if they have a return value,
cannam@167 129 and subroutines in Fortran otherwise.
cannam@167 130
cannam@167 131 </li><li> The ordering of the Fortran array dimensions must be <em>reversed</em>
cannam@167 132 when they are passed to the FFTW plan creation, thanks to differences
cannam@167 133 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@167 134 (see <a href="Fortran_002dinterface-routines.html#Fortran_002dinterface-routines">Fortran-interface routines</a>), which reversed the dimensions
cannam@167 135 for you. See <a href="Reversing-array-dimensions.html#Reversing-array-dimensions">Reversing array dimensions</a>.
cannam@167 136
cannam@167 137 </li><li> <a name="index-alignment-4"></a>
cannam@167 138 <a name="index-SIMD-2"></a>
cannam@167 139 Using ordinary Fortran array declarations like this works, but may
cannam@167 140 yield suboptimal performance because the data may not be not aligned
cannam@167 141 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@167 142 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@167 143
cannam@167 144 </li><li> <a name="index-fftw_005fexecute-5"></a>
cannam@167 145 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@167 146 but rather using the more specialized functions like
cannam@167 147 <code>fftw_execute_dft</code> (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>).
cannam@167 148 However, you should execute the plan on the <code>same arrays</code> as the
cannam@167 149 ones for which you created the plan, unless you are especially
cannam@167 150 careful. See <a href="Plan-execution-in-Fortran.html#Plan-execution-in-Fortran">Plan execution in Fortran</a>. To prevent
cannam@167 151 you from using <code>fftw_execute</code> by mistake, the <code>fftw3.f03</code>
cannam@167 152 file does not provide an <code>fftw_execute</code> interface declaration.
cannam@167 153
cannam@167 154 </li><li> <a name="index-flags-8"></a>
cannam@167 155 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@167 156
cannam@167 157 </li></ul>
cannam@167 158
cannam@167 159 <table class="menu" border="0" cellspacing="0">
cannam@167 160 <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@167 161 </td></tr>
cannam@167 162 </table>
cannam@167 163
cannam@167 164 <hr>
cannam@167 165 <div class="header">
cannam@167 166 <p>
cannam@167 167 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@167 168 </div>
cannam@167 169
cannam@167 170
cannam@167 171
cannam@167 172 </body>
cannam@167 173 </html>