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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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3 <!-- This manual is for FFTW
4 (version 3.3.8, 24 May 2018).
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6 Copyright (C) 2003 Matteo Frigo.
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8 Copyright (C) 2003 Massachusetts Institute of Technology.
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25 <title>FFTW 3.3.8: Words of Wisdom-Saving Plans</title>
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71 <a name="Words-of-Wisdom_002dSaving-Plans"></a>
72 <div class="header">
73 <p>
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>
75 </div>
76 <hr>
77 <a name="Words-of-Wisdom_002d_002d_002dSaving-Plans"></a>
78 <h3 class="section">3.3 Words of Wisdom&mdash;Saving Plans</h3>
79 <a name="index-wisdom"></a>
80 <a name="index-saving-plans-to-disk"></a>
81
82 <p>FFTW implements a method for saving plans to disk and restoring them.
83 In fact, what FFTW does is more general than just saving and loading
84 plans. The mechanism is called <em>wisdom</em>. Here, we describe
85 this feature at a high level. See <a href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>, for a less casual
86 but more complete discussion of how to use wisdom in FFTW.
87 </p>
88 <p>Plans created with the <code>FFTW_MEASURE</code>, <code>FFTW_PATIENT</code>, or
89 <code>FFTW_EXHAUSTIVE</code> options produce near-optimal FFT performance,
90 but may require a long time to compute because FFTW must measure the
91 runtime of many possible plans and select the best one. This setup is
92 designed for the situations where so many transforms of the same size
93 must be computed that the start-up time is irrelevant. For short
94 initialization times, but slower transforms, we have provided
95 <code>FFTW_ESTIMATE</code>. The <code>wisdom</code> mechanism is a way to get the
96 best of both worlds: you compute a good plan once, save it to
97 disk, and later reload it as many times as necessary. The wisdom
98 mechanism can actually save and reload many plans at once, not just
99 one.
100 <a name="index-FFTW_005fMEASURE-1"></a>
101 <a name="index-FFTW_005fPATIENT-1"></a>
102 <a name="index-FFTW_005fEXHAUSTIVE"></a>
103 <a name="index-FFTW_005fESTIMATE-1"></a>
104 </p>
105
106 <p>Whenever you create a plan, the FFTW planner accumulates wisdom, which
107 is information sufficient to reconstruct the plan. After planning,
108 you can save this information to disk by means of the function:
109 </p><div class="example">
110 <pre class="example">int fftw_export_wisdom_to_filename(const char *filename);
111 </pre></div>
112 <a name="index-fftw_005fexport_005fwisdom_005fto_005ffilename"></a>
113 <p>(This function returns non-zero on success.)
114 </p>
115 <p>The next time you run the program, you can restore the wisdom with
116 <code>fftw_import_wisdom_from_filename</code> (which also returns non-zero on success),
117 and then recreate the plan using the same flags as before.
118 </p><div class="example">
119 <pre class="example">int fftw_import_wisdom_from_filename(const char *filename);
120 </pre></div>
121 <a name="index-fftw_005fimport_005fwisdom_005ffrom_005ffilename"></a>
122
123 <p>Wisdom is automatically used for any size to which it is applicable, as
124 long as the planner flags are not more &ldquo;patient&rdquo; than those with which
125 the wisdom was created. For example, wisdom created with
126 <code>FFTW_MEASURE</code> can be used if you later plan with
127 <code>FFTW_ESTIMATE</code> or <code>FFTW_MEASURE</code>, but not with
128 <code>FFTW_PATIENT</code>.
129 </p>
130 <p>The <code>wisdom</code> is cumulative, and is stored in a global, private
131 data structure managed internally by FFTW. The storage space required
132 is minimal, proportional to the logarithm of the sizes the wisdom was
133 generated from. If memory usage is a concern, however, the wisdom can
134 be forgotten and its associated memory freed by calling:
135 </p><div class="example">
136 <pre class="example">void fftw_forget_wisdom(void);
137 </pre></div>
138 <a name="index-fftw_005fforget_005fwisdom"></a>
139
140 <p>Wisdom can be exported to a file, a string, or any other medium.
141 For details, see <a href="Wisdom.html#Wisdom">Wisdom</a>.
142 </p>
143 <hr>
144 <div class="header">
145 <p>
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>
147 </div>
148
149
150
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