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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 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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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: Words of Wisdom-Saving Plans</title>
Chris@82 26
Chris@82 27 <meta name="description" content="FFTW 3.3.8: Words of Wisdom-Saving Plans">
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Chris@82 37 <link href="Caveats-in-Using-Wisdom.html#Caveats-in-Using-Wisdom" rel="next" title="Caveats in Using Wisdom">
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Chris@82 68 </head>
Chris@82 69
Chris@82 70 <body lang="en">
Chris@82 71 <a name="Words-of-Wisdom_002dSaving-Plans"></a>
Chris@82 72 <div class="header">
Chris@82 73 <p>
Chris@82 74 Next: <a href="Caveats-in-Using-Wisdom.html#Caveats-in-Using-Wisdom" accesskey="n" rel="next">Caveats in Using Wisdom</a>, Previous: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="p" rel="prev">Multi-dimensional Array Format</a>, Up: <a href="Other-Important-Topics.html#Other-Important-Topics" accesskey="u" rel="up">Other Important Topics</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="Words-of-Wisdom_002d_002d_002dSaving-Plans"></a>
Chris@82 78 <h3 class="section">3.3 Words of Wisdom&mdash;Saving Plans</h3>
Chris@82 79 <a name="index-wisdom"></a>
Chris@82 80 <a name="index-saving-plans-to-disk"></a>
Chris@82 81
Chris@82 82 <p>FFTW implements a method for saving plans to disk and restoring them.
Chris@82 83 In fact, what FFTW does is more general than just saving and loading
Chris@82 84 plans. The mechanism is called <em>wisdom</em>. Here, we describe
Chris@82 85 this feature at a high level. See <a href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>, for a less casual
Chris@82 86 but more complete discussion of how to use wisdom in FFTW.
Chris@82 87 </p>
Chris@82 88 <p>Plans created with the <code>FFTW_MEASURE</code>, <code>FFTW_PATIENT</code>, or
Chris@82 89 <code>FFTW_EXHAUSTIVE</code> options produce near-optimal FFT performance,
Chris@82 90 but may require a long time to compute because FFTW must measure the
Chris@82 91 runtime of many possible plans and select the best one. This setup is
Chris@82 92 designed for the situations where so many transforms of the same size
Chris@82 93 must be computed that the start-up time is irrelevant. For short
Chris@82 94 initialization times, but slower transforms, we have provided
Chris@82 95 <code>FFTW_ESTIMATE</code>. The <code>wisdom</code> mechanism is a way to get the
Chris@82 96 best of both worlds: you compute a good plan once, save it to
Chris@82 97 disk, and later reload it as many times as necessary. The wisdom
Chris@82 98 mechanism can actually save and reload many plans at once, not just
Chris@82 99 one.
Chris@82 100 <a name="index-FFTW_005fMEASURE-1"></a>
Chris@82 101 <a name="index-FFTW_005fPATIENT-1"></a>
Chris@82 102 <a name="index-FFTW_005fEXHAUSTIVE"></a>
Chris@82 103 <a name="index-FFTW_005fESTIMATE-1"></a>
Chris@82 104 </p>
Chris@82 105
Chris@82 106 <p>Whenever you create a plan, the FFTW planner accumulates wisdom, which
Chris@82 107 is information sufficient to reconstruct the plan. After planning,
Chris@82 108 you can save this information to disk by means of the function:
Chris@82 109 </p><div class="example">
Chris@82 110 <pre class="example">int fftw_export_wisdom_to_filename(const char *filename);
Chris@82 111 </pre></div>
Chris@82 112 <a name="index-fftw_005fexport_005fwisdom_005fto_005ffilename"></a>
Chris@82 113 <p>(This function returns non-zero on success.)
Chris@82 114 </p>
Chris@82 115 <p>The next time you run the program, you can restore the wisdom with
Chris@82 116 <code>fftw_import_wisdom_from_filename</code> (which also returns non-zero on success),
Chris@82 117 and then recreate the plan using the same flags as before.
Chris@82 118 </p><div class="example">
Chris@82 119 <pre class="example">int fftw_import_wisdom_from_filename(const char *filename);
Chris@82 120 </pre></div>
Chris@82 121 <a name="index-fftw_005fimport_005fwisdom_005ffrom_005ffilename"></a>
Chris@82 122
Chris@82 123 <p>Wisdom is automatically used for any size to which it is applicable, as
Chris@82 124 long as the planner flags are not more &ldquo;patient&rdquo; than those with which
Chris@82 125 the wisdom was created. For example, wisdom created with
Chris@82 126 <code>FFTW_MEASURE</code> can be used if you later plan with
Chris@82 127 <code>FFTW_ESTIMATE</code> or <code>FFTW_MEASURE</code>, but not with
Chris@82 128 <code>FFTW_PATIENT</code>.
Chris@82 129 </p>
Chris@82 130 <p>The <code>wisdom</code> is cumulative, and is stored in a global, private
Chris@82 131 data structure managed internally by FFTW. The storage space required
Chris@82 132 is minimal, proportional to the logarithm of the sizes the wisdom was
Chris@82 133 generated from. If memory usage is a concern, however, the wisdom can
Chris@82 134 be forgotten and its associated memory freed by calling:
Chris@82 135 </p><div class="example">
Chris@82 136 <pre class="example">void fftw_forget_wisdom(void);
Chris@82 137 </pre></div>
Chris@82 138 <a name="index-fftw_005fforget_005fwisdom"></a>
Chris@82 139
Chris@82 140 <p>Wisdom can be exported to a file, a string, or any other medium.
Chris@82 141 For details, see <a href="Wisdom.html#Wisdom">Wisdom</a>.
Chris@82 142 </p>
Chris@82 143 <hr>
Chris@82 144 <div class="header">
Chris@82 145 <p>
Chris@82 146 Next: <a href="Caveats-in-Using-Wisdom.html#Caveats-in-Using-Wisdom" accesskey="n" rel="next">Caveats in Using Wisdom</a>, Previous: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="p" rel="prev">Multi-dimensional Array Format</a>, Up: <a href="Other-Important-Topics.html#Other-Important-Topics" accesskey="u" rel="up">Other Important Topics</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@82 147 </div>
Chris@82 148
Chris@82 149
Chris@82 150
Chris@82 151 </body>
Chris@82 152 </html>