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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 bd3cc4d1df30
children
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
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cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: Words of Wisdom-Saving Plans</title>
cannam@167 26
cannam@167 27 <meta name="description" content="FFTW 3.3.8: Words of Wisdom-Saving Plans">
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cannam@167 37 <link href="Caveats-in-Using-Wisdom.html#Caveats-in-Using-Wisdom" rel="next" title="Caveats in Using Wisdom">
cannam@167 38 <link href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way" rel="prev" title="Dynamic Arrays in C-The Wrong Way">
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cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="Words-of-Wisdom_002dSaving-Plans"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 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>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="Words-of-Wisdom_002d_002d_002dSaving-Plans"></a>
cannam@167 78 <h3 class="section">3.3 Words of Wisdom&mdash;Saving Plans</h3>
cannam@167 79 <a name="index-wisdom"></a>
cannam@167 80 <a name="index-saving-plans-to-disk"></a>
cannam@167 81
cannam@167 82 <p>FFTW implements a method for saving plans to disk and restoring them.
cannam@167 83 In fact, what FFTW does is more general than just saving and loading
cannam@167 84 plans. The mechanism is called <em>wisdom</em>. Here, we describe
cannam@167 85 this feature at a high level. See <a href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>, for a less casual
cannam@167 86 but more complete discussion of how to use wisdom in FFTW.
cannam@167 87 </p>
cannam@167 88 <p>Plans created with the <code>FFTW_MEASURE</code>, <code>FFTW_PATIENT</code>, or
cannam@167 89 <code>FFTW_EXHAUSTIVE</code> options produce near-optimal FFT performance,
cannam@167 90 but may require a long time to compute because FFTW must measure the
cannam@167 91 runtime of many possible plans and select the best one. This setup is
cannam@167 92 designed for the situations where so many transforms of the same size
cannam@167 93 must be computed that the start-up time is irrelevant. For short
cannam@167 94 initialization times, but slower transforms, we have provided
cannam@167 95 <code>FFTW_ESTIMATE</code>. The <code>wisdom</code> mechanism is a way to get the
cannam@167 96 best of both worlds: you compute a good plan once, save it to
cannam@167 97 disk, and later reload it as many times as necessary. The wisdom
cannam@167 98 mechanism can actually save and reload many plans at once, not just
cannam@167 99 one.
cannam@167 100 <a name="index-FFTW_005fMEASURE-1"></a>
cannam@167 101 <a name="index-FFTW_005fPATIENT-1"></a>
cannam@167 102 <a name="index-FFTW_005fEXHAUSTIVE"></a>
cannam@167 103 <a name="index-FFTW_005fESTIMATE-1"></a>
cannam@167 104 </p>
cannam@167 105
cannam@167 106 <p>Whenever you create a plan, the FFTW planner accumulates wisdom, which
cannam@167 107 is information sufficient to reconstruct the plan. After planning,
cannam@167 108 you can save this information to disk by means of the function:
cannam@167 109 </p><div class="example">
cannam@167 110 <pre class="example">int fftw_export_wisdom_to_filename(const char *filename);
cannam@167 111 </pre></div>
cannam@167 112 <a name="index-fftw_005fexport_005fwisdom_005fto_005ffilename"></a>
cannam@167 113 <p>(This function returns non-zero on success.)
cannam@167 114 </p>
cannam@167 115 <p>The next time you run the program, you can restore the wisdom with
cannam@167 116 <code>fftw_import_wisdom_from_filename</code> (which also returns non-zero on success),
cannam@167 117 and then recreate the plan using the same flags as before.
cannam@167 118 </p><div class="example">
cannam@167 119 <pre class="example">int fftw_import_wisdom_from_filename(const char *filename);
cannam@167 120 </pre></div>
cannam@167 121 <a name="index-fftw_005fimport_005fwisdom_005ffrom_005ffilename"></a>
cannam@167 122
cannam@167 123 <p>Wisdom is automatically used for any size to which it is applicable, as
cannam@167 124 long as the planner flags are not more &ldquo;patient&rdquo; than those with which
cannam@167 125 the wisdom was created. For example, wisdom created with
cannam@167 126 <code>FFTW_MEASURE</code> can be used if you later plan with
cannam@167 127 <code>FFTW_ESTIMATE</code> or <code>FFTW_MEASURE</code>, but not with
cannam@167 128 <code>FFTW_PATIENT</code>.
cannam@167 129 </p>
cannam@167 130 <p>The <code>wisdom</code> is cumulative, and is stored in a global, private
cannam@167 131 data structure managed internally by FFTW. The storage space required
cannam@167 132 is minimal, proportional to the logarithm of the sizes the wisdom was
cannam@167 133 generated from. If memory usage is a concern, however, the wisdom can
cannam@167 134 be forgotten and its associated memory freed by calling:
cannam@167 135 </p><div class="example">
cannam@167 136 <pre class="example">void fftw_forget_wisdom(void);
cannam@167 137 </pre></div>
cannam@167 138 <a name="index-fftw_005fforget_005fwisdom"></a>
cannam@167 139
cannam@167 140 <p>Wisdom can be exported to a file, a string, or any other medium.
cannam@167 141 For details, see <a href="Wisdom.html#Wisdom">Wisdom</a>.
cannam@167 142 </p>
cannam@167 143 <hr>
cannam@167 144 <div class="header">
cannam@167 145 <p>
cannam@167 146 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>
cannam@167 147 </div>
cannam@167 148
cannam@167 149
cannam@167 150
cannam@167 151 </body>
cannam@167 152 </html>