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1 <html lang="en">
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2 <head>
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3 <title>Using Plans - 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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6 <meta name="generator" content="makeinfo 4.13">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="FFTW-Reference.html#FFTW-Reference" title="FFTW Reference">
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9 <link rel="prev" href="Data-Types-and-Files.html#Data-Types-and-Files" title="Data Types and Files">
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10 <link rel="next" href="Basic-Interface.html#Basic-Interface" title="Basic Interface">
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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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35 <style type="text/css"><!--
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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="Using-Plans"></a>
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50 <p>
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51 Next: <a rel="next" accesskey="n" href="Basic-Interface.html#Basic-Interface">Basic Interface</a>,
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52 Previous: <a rel="previous" accesskey="p" href="Data-Types-and-Files.html#Data-Types-and-Files">Data Types and Files</a>,
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53 Up: <a rel="up" accesskey="u" href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>
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54 <hr>
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55 </div>
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56
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57 <h3 class="section">4.2 Using Plans</h3>
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58
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59 <p>Plans for all transform types in FFTW are stored as type
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60 <code>fftw_plan</code> (an opaque pointer type), and are created by one of the
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61 various planning routines described in the following sections.
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62 <a name="index-fftw_005fplan-152"></a>An <code>fftw_plan</code> contains all information necessary to compute the
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63 transform, including the pointers to the input and output arrays.
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64
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65 <pre class="example"> void fftw_execute(const fftw_plan plan);
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66 </pre>
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67 <p><a name="index-fftw_005fexecute-153"></a>
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68 This executes the <code>plan</code>, to compute the corresponding transform on
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69 the arrays for which it was planned (which must still exist). The plan
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70 is not modified, and <code>fftw_execute</code> can be called as many times as
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71 desired.
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72
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73 <p>To apply a given plan to a different array, you can use the new-array execute
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74 interface. See <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>.
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75
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76 <p><code>fftw_execute</code> (and equivalents) is the only function in FFTW
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77 guaranteed to be thread-safe; see <a href="Thread-safety.html#Thread-safety">Thread safety</a>.
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78
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79 <p>This function:
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80 <pre class="example"> void fftw_destroy_plan(fftw_plan plan);
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81 </pre>
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82 <p><a name="index-fftw_005fdestroy_005fplan-154"></a>deallocates the <code>plan</code> and all its associated data.
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83
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84 <p>FFTW's planner saves some other persistent data, such as the
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85 accumulated wisdom and a list of algorithms available in the current
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86 configuration. If you want to deallocate all of that and reset FFTW
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87 to the pristine state it was in when you started your program, you can
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88 call:
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89
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90 <pre class="example"> void fftw_cleanup(void);
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91 </pre>
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92 <p><a name="index-fftw_005fcleanup-155"></a>
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93 After calling <code>fftw_cleanup</code>, all existing plans become undefined,
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94 and you should not attempt to execute them nor to destroy them. You can
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95 however create and execute/destroy new plans, in which case FFTW starts
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96 accumulating wisdom information again.
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97
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98 <p><code>fftw_cleanup</code> does not deallocate your plans, however. To prevent
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99 memory leaks, you must still call <code>fftw_destroy_plan</code> before
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100 executing <code>fftw_cleanup</code>.
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101
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102 <p>Occasionally, it may useful to know FFTW's internal “cost” metric
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103 that it uses to compare plans to one another; this cost is
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104 proportional to an execution time of the plan, in undocumented units,
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105 if the plan was created with the <code>FFTW_MEASURE</code> or other
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106 timing-based options, or alternatively is a heuristic cost function
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107 for <code>FFTW_ESTIMATE</code> plans. (The cost values of measured and
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108 estimated plans are not comparable, being in different units. Also,
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109 costs from different FFTW versions or the same version compiled
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110 differently may not be in the same units. Plans created from wisdom
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111 have a cost of 0 since no timing measurement is performed for them.
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112 Finally, certain problems for which only one top-level algorithm was
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113 possible may have required no measurements of the cost of the whole
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114 plan, in which case <code>fftw_cost</code> will also return 0.) The cost
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115 metric for a given plan is returned by:
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116
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117 <pre class="example"> double fftw_cost(const fftw_plan plan);
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118 </pre>
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119 <p><a name="index-fftw_005fcost-156"></a>
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120 The following two routines are provided purely for academic purposes
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121 (that is, for entertainment).
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122
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123 <pre class="example"> void fftw_flops(const fftw_plan plan,
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124 double *add, double *mul, double *fma);
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125 </pre>
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126 <p><a name="index-fftw_005fflops-157"></a>
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127 Given a <code>plan</code>, set <code>add</code>, <code>mul</code>, and <code>fma</code> to an
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128 exact count of the number of floating-point additions, multiplications,
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129 and fused multiply-add operations involved in the plan's execution. The
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130 total number of floating-point operations (flops) is <code>add + mul +
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131 2*fma</code>, or <code>add + mul + fma</code> if the hardware supports fused
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132 multiply-add instructions (although the number of FMA operations is only
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133 approximate because of compiler voodoo). (The number of operations
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134 should be an integer, but we use <code>double</code> to avoid overflowing
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135 <code>int</code> for large transforms; the arguments are of type <code>double</code>
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136 even for single and long-double precision versions of FFTW.)
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137
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138 <pre class="example"> void fftw_fprint_plan(const fftw_plan plan, FILE *output_file);
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139 void fftw_print_plan(const fftw_plan plan);
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140 </pre>
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141 <p><a name="index-fftw_005ffprint_005fplan-158"></a><a name="index-fftw_005fprint_005fplan-159"></a>
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142 This outputs a “nerd-readable” representation of the <code>plan</code> to
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143 the given file or to <code>stdout</code>, respectively.
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144
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145 <!-- -->
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146 </body></html>
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147
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