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2 <head>
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3 <title>Fortran-interface routines - FFTW 3.3.3</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.3.3">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" title="Calling FFTW from Legacy Fortran">
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9 <link rel="prev" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran" title="Calling FFTW from Legacy Fortran">
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10 <link rel="next" href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran" title="FFTW Constants in Fortran">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.3.3, 25 November 2012).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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33 -->
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <a name="Fortran-interface-routines"></a>
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50 <a name="Fortran_002dinterface-routines"></a>
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51 <p>
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52 Next: <a rel="next" accesskey="n" href="FFTW-Constants-in-Fortran.html#FFTW-Constants-in-Fortran">FFTW Constants in Fortran</a>,
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53 Previous: <a rel="previous" accesskey="p" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran">Calling FFTW from Legacy Fortran</a>,
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54 Up: <a rel="up" accesskey="u" href="Calling-FFTW-from-Legacy-Fortran.html#Calling-FFTW-from-Legacy-Fortran">Calling FFTW from Legacy Fortran</a>
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55 <hr>
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56 </div>
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57
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58 <h3 class="section">8.1 Fortran-interface routines</h3>
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59
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60 <p>Nearly all of the FFTW functions have Fortran-callable equivalents.
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61 The name of the legacy Fortran routine is the same as that of the
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62 corresponding C routine, but with the ‘<samp><span class="samp">fftw_</span></samp>’ prefix replaced by
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63 ‘<samp><span class="samp">dfftw_</span></samp>’.<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a> The single and long-double precision
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64 versions use ‘<samp><span class="samp">sfftw_</span></samp>’ and ‘<samp><span class="samp">lfftw_</span></samp>’, respectively, instead of
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65 ‘<samp><span class="samp">fftwf_</span></samp>’ and ‘<samp><span class="samp">fftwl_</span></samp>’; quadruple precision (<code>real*16</code>)
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66 is available on some systems as ‘<samp><span class="samp">fftwq_</span></samp>’ (see <a href="Precision.html#Precision">Precision</a>).
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67 (Note that <code>long double</code> on x86 hardware is usually at most
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68 80-bit extended precision, <em>not</em> quadruple precision.)
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69
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70 <p>For the most part, all of the arguments to the functions are the same,
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71 with the following exceptions:
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72
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73 <ul>
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74 <li><code>plan</code> variables (what would be of type <code>fftw_plan</code> in C),
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75 must be declared as a type that is at least as big as a pointer
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76 (address) on your machine. We recommend using <code>integer*8</code> everywhere,
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77 since this should always be big enough.
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78 <a name="index-portability-578"></a>
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79 <li>Any function that returns a value (e.g. <code>fftw_plan_dft</code>) is
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80 converted into a <em>subroutine</em>. The return value is converted into
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81 an additional <em>first</em> parameter of this subroutine.<a rel="footnote" href="#fn-2" name="fnd-2"><sup>2</sup></a>
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82
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83 <li><a name="index-column_002dmajor-579"></a>The Fortran routines expect multi-dimensional arrays to be in
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84 <em>column-major</em> order, which is the ordinary format of Fortran
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85 arrays (see <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>). They do this
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86 transparently and costlessly simply by reversing the order of the
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87 dimensions passed to FFTW, but this has one important consequence for
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88 multi-dimensional real-complex transforms, discussed below.
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89
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90 <li>Wisdom import and export is somewhat more tricky because one cannot
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91 easily pass files or strings between C and Fortran; see <a href="Wisdom-of-Fortran_003f.html#Wisdom-of-Fortran_003f">Wisdom of Fortran?</a>.
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92
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93 <li>Legacy Fortran cannot use the <code>fftw_malloc</code> dynamic-allocation routine.
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94 If you want to exploit the SIMD FFTW (see <a href="SIMD-alignment-and-fftw_005fmalloc.html#SIMD-alignment-and-fftw_005fmalloc">SIMD alignment and fftw_malloc</a>), you'll
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95 need to figure out some other way to ensure that your arrays are at
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96 least 16-byte aligned.
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97
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98 <li><a name="index-fftw_005fiodim-580"></a><a name="index-guru-interface-581"></a>Since Fortran 77 does not have data structures, the <code>fftw_iodim</code>
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99 structure from the guru interface (see <a href="Guru-vector-and-transform-sizes.html#Guru-vector-and-transform-sizes">Guru vector and transform sizes</a>) must be split into separate arguments. In particular, any
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100 <code>fftw_iodim</code> array arguments in the C guru interface become three
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101 integer array arguments (<code>n</code>, <code>is</code>, and <code>os</code>) in the
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102 Fortran guru interface, all of whose lengths should be equal to the
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103 corresponding <code>rank</code> argument.
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104
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105 <li>The guru planner interface in Fortran does <em>not</em> do any automatic
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106 translation between column-major and row-major; you are responsible
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107 for setting the strides etcetera to correspond to your Fortran arrays.
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108 However, as a slight bug that we are preserving for backwards
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109 compatibility, the ‘<samp><span class="samp">plan_guru_r2r</span></samp>’ in Fortran <em>does</em> reverse the
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110 order of its <code>kind</code> array parameter, so the <code>kind</code> array
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111 of that routine should be in the reverse of the order of the iodim
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112 arrays (see above).
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113
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114 </ul>
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115
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116 <p>In general, you should take care to use Fortran data types that
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117 correspond to (i.e. are the same size as) the C types used by FFTW.
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118 In practice, this correspondence is usually straightforward
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119 (i.e. <code>integer</code> corresponds to <code>int</code>, <code>real</code>
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120 corresponds to <code>float</code>, etcetera). The native Fortran
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121 double/single-precision complex type should be compatible with
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122 <code>fftw_complex</code>/<code>fftwf_complex</code>. Such simple correspondences
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123 are assumed in the examples below.
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124 <a name="index-portability-582"></a>
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125 <!-- -->
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126
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127 <div class="footnote">
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128 <hr>
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129 <h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Technically, Fortran 77 identifiers are not
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130 allowed to have more than 6 characters, nor may they contain
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131 underscores. Any compiler that enforces this limitation doesn't
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132 deserve to link to FFTW.</p>
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133
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134 <p class="footnote"><small>[<a name="fn-2" href="#fnd-2">2</a>]</small> The
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135 reason for this is that some Fortran implementations seem to have
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136 trouble with C function return values, and vice versa.</p>
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137
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138 <hr></div>
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139
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140 </body></html>
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141
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