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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam
date Tue, 19 Nov 2019 14:52:55 +0000
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Chris@82 3 <!-- This manual is for FFTW
Chris@82 4 (version 3.3.8, 24 May 2018).
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Chris@82 6 Copyright (C) 2003 Matteo Frigo.
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Chris@82 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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Chris@82 24 <head>
Chris@82 25 <title>FFTW 3.3.8: Using Plans</title>
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Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Using-Plans"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Basic-Interface.html#Basic-Interface" accesskey="n" rel="next">Basic Interface</a>, Previous: <a href="Data-Types-and-Files.html#Data-Types-and-Files" accesskey="p" rel="prev">Data Types and Files</a>, Up: <a href="FFTW-Reference.html#FFTW-Reference" accesskey="u" rel="up">FFTW Reference</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>
Chris@82 75 </div>
Chris@82 76 <hr>
Chris@82 77 <a name="Using-Plans-1"></a>
Chris@82 78 <h3 class="section">4.2 Using Plans</h3>
Chris@82 79
Chris@82 80 <p>Plans for all transform types in FFTW are stored as type
Chris@82 81 <code>fftw_plan</code> (an opaque pointer type), and are created by one of the
Chris@82 82 various planning routines described in the following sections.
Chris@82 83 <a name="index-fftw_005fplan-1"></a>
Chris@82 84 An <code>fftw_plan</code> contains all information necessary to compute the
Chris@82 85 transform, including the pointers to the input and output arrays.
Chris@82 86 </p>
Chris@82 87 <div class="example">
Chris@82 88 <pre class="example">void fftw_execute(const fftw_plan plan);
Chris@82 89 </pre></div>
Chris@82 90 <a name="index-fftw_005fexecute-1"></a>
Chris@82 91
Chris@82 92 <p>This executes the <code>plan</code>, to compute the corresponding transform on
Chris@82 93 the arrays for which it was planned (which must still exist). The plan
Chris@82 94 is not modified, and <code>fftw_execute</code> can be called as many times as
Chris@82 95 desired.
Chris@82 96 </p>
Chris@82 97 <p>To apply a given plan to a different array, you can use the new-array execute
Chris@82 98 interface. See <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>.
Chris@82 99 </p>
Chris@82 100 <p><code>fftw_execute</code> (and equivalents) is the only function in FFTW
Chris@82 101 guaranteed to be thread-safe; see <a href="Thread-safety.html#Thread-safety">Thread safety</a>.
Chris@82 102 </p>
Chris@82 103 <p>This function:
Chris@82 104 </p><div class="example">
Chris@82 105 <pre class="example">void fftw_destroy_plan(fftw_plan plan);
Chris@82 106 </pre></div>
Chris@82 107 <a name="index-fftw_005fdestroy_005fplan-1"></a>
Chris@82 108 <p>deallocates the <code>plan</code> and all its associated data.
Chris@82 109 </p>
Chris@82 110 <p>FFTW&rsquo;s planner saves some other persistent data, such as the
Chris@82 111 accumulated wisdom and a list of algorithms available in the current
Chris@82 112 configuration. If you want to deallocate all of that and reset FFTW
Chris@82 113 to the pristine state it was in when you started your program, you can
Chris@82 114 call:
Chris@82 115 </p>
Chris@82 116 <div class="example">
Chris@82 117 <pre class="example">void fftw_cleanup(void);
Chris@82 118 </pre></div>
Chris@82 119 <a name="index-fftw_005fcleanup"></a>
Chris@82 120
Chris@82 121 <p>After calling <code>fftw_cleanup</code>, all existing plans become undefined,
Chris@82 122 and you should not attempt to execute them nor to destroy them. You can
Chris@82 123 however create and execute/destroy new plans, in which case FFTW starts
Chris@82 124 accumulating wisdom information again.
Chris@82 125 </p>
Chris@82 126 <p><code>fftw_cleanup</code> does not deallocate your plans, however. To prevent
Chris@82 127 memory leaks, you must still call <code>fftw_destroy_plan</code> before
Chris@82 128 executing <code>fftw_cleanup</code>.
Chris@82 129 </p>
Chris@82 130 <p>Occasionally, it may useful to know FFTW&rsquo;s internal &ldquo;cost&rdquo; metric
Chris@82 131 that it uses to compare plans to one another; this cost is
Chris@82 132 proportional to an execution time of the plan, in undocumented units,
Chris@82 133 if the plan was created with the <code>FFTW_MEASURE</code> or other
Chris@82 134 timing-based options, or alternatively is a heuristic cost function
Chris@82 135 for <code>FFTW_ESTIMATE</code> plans. (The cost values of measured and
Chris@82 136 estimated plans are not comparable, being in different units. Also,
Chris@82 137 costs from different FFTW versions or the same version compiled
Chris@82 138 differently may not be in the same units. Plans created from wisdom
Chris@82 139 have a cost of 0 since no timing measurement is performed for them.
Chris@82 140 Finally, certain problems for which only one top-level algorithm was
Chris@82 141 possible may have required no measurements of the cost of the whole
Chris@82 142 plan, in which case <code>fftw_cost</code> will also return 0.) The cost
Chris@82 143 metric for a given plan is returned by:
Chris@82 144 </p>
Chris@82 145 <div class="example">
Chris@82 146 <pre class="example">double fftw_cost(const fftw_plan plan);
Chris@82 147 </pre></div>
Chris@82 148 <a name="index-fftw_005fcost"></a>
Chris@82 149
Chris@82 150 <p>The following two routines are provided purely for academic purposes
Chris@82 151 (that is, for entertainment).
Chris@82 152 </p>
Chris@82 153 <div class="example">
Chris@82 154 <pre class="example">void fftw_flops(const fftw_plan plan,
Chris@82 155 double *add, double *mul, double *fma);
Chris@82 156 </pre></div>
Chris@82 157 <a name="index-fftw_005fflops"></a>
Chris@82 158
Chris@82 159 <p>Given a <code>plan</code>, set <code>add</code>, <code>mul</code>, and <code>fma</code> to an
Chris@82 160 exact count of the number of floating-point additions, multiplications,
Chris@82 161 and fused multiply-add operations involved in the plan&rsquo;s execution. The
Chris@82 162 total number of floating-point operations (flops) is <code>add + mul +
Chris@82 163 2*fma</code>, or <code>add + mul + fma</code> if the hardware supports fused
Chris@82 164 multiply-add instructions (although the number of FMA operations is only
Chris@82 165 approximate because of compiler voodoo). (The number of operations
Chris@82 166 should be an integer, but we use <code>double</code> to avoid overflowing
Chris@82 167 <code>int</code> for large transforms; the arguments are of type <code>double</code>
Chris@82 168 even for single and long-double precision versions of FFTW.)
Chris@82 169 </p>
Chris@82 170 <div class="example">
Chris@82 171 <pre class="example">void fftw_fprint_plan(const fftw_plan plan, FILE *output_file);
Chris@82 172 void fftw_print_plan(const fftw_plan plan);
Chris@82 173 char *fftw_sprint_plan(const fftw_plan plan);
Chris@82 174 </pre></div>
Chris@82 175 <a name="index-fftw_005ffprint_005fplan"></a>
Chris@82 176 <a name="index-fftw_005fprint_005fplan"></a>
Chris@82 177
Chris@82 178 <p>This outputs a &ldquo;nerd-readable&rdquo; representation of the <code>plan</code> to
Chris@82 179 the given file, to <code>stdout</code>, or two a newly allocated
Chris@82 180 NUL-terminated string (which the caller is responsible for deallocating
Chris@82 181 with <code>free</code>), respectively.
Chris@82 182 </p>
Chris@82 183 <hr>
Chris@82 184 <div class="header">
Chris@82 185 <p>
Chris@82 186 Next: <a href="Basic-Interface.html#Basic-Interface" accesskey="n" rel="next">Basic Interface</a>, Previous: <a href="Data-Types-and-Files.html#Data-Types-and-Files" accesskey="p" rel="prev">Data Types and Files</a>, Up: <a href="FFTW-Reference.html#FFTW-Reference" accesskey="u" rel="up">FFTW Reference</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>
Chris@82 187 </div>
Chris@82 188
Chris@82 189
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