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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 7867fa7e1b6b
children
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cannam@127 3 <!-- This manual is for FFTW
cannam@127 4 (version 3.3.5, 30 July 2016).
cannam@127 5
cannam@127 6 Copyright (C) 2003 Matteo Frigo.
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cannam@127 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@127 24 <head>
cannam@127 25 <title>FFTW 3.3.5: Words of Wisdom-Saving Plans</title>
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cannam@127 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
cannam@127 72 <a name="Words-of-Wisdom_002dSaving-Plans"></a>
cannam@127 73 <div class="header">
cannam@127 74 <p>
cannam@127 75 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>
cannam@127 76 </div>
cannam@127 77 <hr>
cannam@127 78 <a name="Words-of-Wisdom_002d_002d_002dSaving-Plans"></a>
cannam@127 79 <h3 class="section">3.3 Words of Wisdom&mdash;Saving Plans</h3>
cannam@127 80 <a name="index-wisdom"></a>
cannam@127 81 <a name="index-saving-plans-to-disk"></a>
cannam@127 82
cannam@127 83 <p>FFTW implements a method for saving plans to disk and restoring them.
cannam@127 84 In fact, what FFTW does is more general than just saving and loading
cannam@127 85 plans. The mechanism is called <em>wisdom</em>. Here, we describe
cannam@127 86 this feature at a high level. See <a href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>, for a less casual
cannam@127 87 but more complete discussion of how to use wisdom in FFTW.
cannam@127 88 </p>
cannam@127 89 <p>Plans created with the <code>FFTW_MEASURE</code>, <code>FFTW_PATIENT</code>, or
cannam@127 90 <code>FFTW_EXHAUSTIVE</code> options produce near-optimal FFT performance,
cannam@127 91 but may require a long time to compute because FFTW must measure the
cannam@127 92 runtime of many possible plans and select the best one. This setup is
cannam@127 93 designed for the situations where so many transforms of the same size
cannam@127 94 must be computed that the start-up time is irrelevant. For short
cannam@127 95 initialization times, but slower transforms, we have provided
cannam@127 96 <code>FFTW_ESTIMATE</code>. The <code>wisdom</code> mechanism is a way to get the
cannam@127 97 best of both worlds: you compute a good plan once, save it to
cannam@127 98 disk, and later reload it as many times as necessary. The wisdom
cannam@127 99 mechanism can actually save and reload many plans at once, not just
cannam@127 100 one.
cannam@127 101 <a name="index-FFTW_005fMEASURE-1"></a>
cannam@127 102 <a name="index-FFTW_005fPATIENT-1"></a>
cannam@127 103 <a name="index-FFTW_005fEXHAUSTIVE"></a>
cannam@127 104 <a name="index-FFTW_005fESTIMATE-1"></a>
cannam@127 105 </p>
cannam@127 106
cannam@127 107 <p>Whenever you create a plan, the FFTW planner accumulates wisdom, which
cannam@127 108 is information sufficient to reconstruct the plan. After planning,
cannam@127 109 you can save this information to disk by means of the function:
cannam@127 110 </p><div class="example">
cannam@127 111 <pre class="example">int fftw_export_wisdom_to_filename(const char *filename);
cannam@127 112 </pre></div>
cannam@127 113 <a name="index-fftw_005fexport_005fwisdom_005fto_005ffilename"></a>
cannam@127 114 <p>(This function returns non-zero on success.)
cannam@127 115 </p>
cannam@127 116 <p>The next time you run the program, you can restore the wisdom with
cannam@127 117 <code>fftw_import_wisdom_from_filename</code> (which also returns non-zero on success),
cannam@127 118 and then recreate the plan using the same flags as before.
cannam@127 119 </p><div class="example">
cannam@127 120 <pre class="example">int fftw_import_wisdom_from_filename(const char *filename);
cannam@127 121 </pre></div>
cannam@127 122 <a name="index-fftw_005fimport_005fwisdom_005ffrom_005ffilename"></a>
cannam@127 123
cannam@127 124 <p>Wisdom is automatically used for any size to which it is applicable, as
cannam@127 125 long as the planner flags are not more &ldquo;patient&rdquo; than those with which
cannam@127 126 the wisdom was created. For example, wisdom created with
cannam@127 127 <code>FFTW_MEASURE</code> can be used if you later plan with
cannam@127 128 <code>FFTW_ESTIMATE</code> or <code>FFTW_MEASURE</code>, but not with
cannam@127 129 <code>FFTW_PATIENT</code>.
cannam@127 130 </p>
cannam@127 131 <p>The <code>wisdom</code> is cumulative, and is stored in a global, private
cannam@127 132 data structure managed internally by FFTW. The storage space required
cannam@127 133 is minimal, proportional to the logarithm of the sizes the wisdom was
cannam@127 134 generated from. If memory usage is a concern, however, the wisdom can
cannam@127 135 be forgotten and its associated memory freed by calling:
cannam@127 136 </p><div class="example">
cannam@127 137 <pre class="example">void fftw_forget_wisdom(void);
cannam@127 138 </pre></div>
cannam@127 139 <a name="index-fftw_005fforget_005fwisdom"></a>
cannam@127 140
cannam@127 141 <p>Wisdom can be exported to a file, a string, or any other medium.
cannam@127 142 For details, see <a href="Wisdom.html#Wisdom">Wisdom</a>.
cannam@127 143 </p>
cannam@127 144 <hr>
cannam@127 145 <div class="header">
cannam@127 146 <p>
cannam@127 147 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>
cannam@127 148 </div>
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cannam@127 150
cannam@127 151
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