mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-15 01:05:06 +00:00
141 lines
6.9 KiB
HTML
141 lines
6.9 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- This manual is for FFTW
|
|
(version 3.3.10, 10 December 2020).
|
|
|
|
Copyright (C) 2003 Matteo Frigo.
|
|
|
|
Copyright (C) 2003 Massachusetts Institute of Technology.
|
|
|
|
Permission is granted to make and distribute verbatim copies of this
|
|
manual provided the copyright notice and this permission notice are
|
|
preserved on all copies.
|
|
|
|
Permission is granted to copy and distribute modified versions of this
|
|
manual under the conditions for verbatim copying, provided that the
|
|
entire resulting derived work is distributed under the terms of a
|
|
permission notice identical to this one.
|
|
|
|
Permission is granted to copy and distribute translations of this manual
|
|
into another language, under the above conditions for modified versions,
|
|
except that this permission notice may be stated in a translation
|
|
approved by the Free Software Foundation. -->
|
|
<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>Words of Wisdom-Saving Plans (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Words of Wisdom-Saving Plans (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Words of Wisdom-Saving Plans (FFTW 3.3.10)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Other-Important-Topics.html" rel="up" title="Other Important Topics">
|
|
<link href="Caveats-in-Using-Wisdom.html" rel="next" title="Caveats in Using Wisdom">
|
|
<link href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html" rel="prev" title="Dynamic Arrays in C-The Wrong Way">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<span id="Words-of-Wisdom_002dSaving-Plans"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Caveats-in-Using-Wisdom.html" accesskey="n" rel="next">Caveats in Using Wisdom</a>, Previous: <a href="Multi_002ddimensional-Array-Format.html" accesskey="p" rel="prev">Multi-dimensional Array Format</a>, Up: <a href="Other-Important-Topics.html" accesskey="u" rel="up">Other Important Topics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<span id="Words-of-Wisdom_002d_002d_002dSaving-Plans"></span><h3 class="section">3.3 Words of Wisdom—Saving Plans</h3>
|
|
<span id="index-wisdom"></span>
|
|
<span id="index-saving-plans-to-disk"></span>
|
|
|
|
<p>FFTW implements a method for saving plans to disk and restoring them.
|
|
In fact, what FFTW does is more general than just saving and loading
|
|
plans. The mechanism is called <em>wisdom</em>. Here, we describe
|
|
this feature at a high level. See <a href="FFTW-Reference.html">FFTW Reference</a>, for a less casual
|
|
but more complete discussion of how to use wisdom in FFTW.
|
|
</p>
|
|
<p>Plans created with the <code>FFTW_MEASURE</code>, <code>FFTW_PATIENT</code>, or
|
|
<code>FFTW_EXHAUSTIVE</code> options produce near-optimal FFT performance,
|
|
but may require a long time to compute because FFTW must measure the
|
|
runtime of many possible plans and select the best one. This setup is
|
|
designed for the situations where so many transforms of the same size
|
|
must be computed that the start-up time is irrelevant. For short
|
|
initialization times, but slower transforms, we have provided
|
|
<code>FFTW_ESTIMATE</code>. The <code>wisdom</code> mechanism is a way to get the
|
|
best of both worlds: you compute a good plan once, save it to
|
|
disk, and later reload it as many times as necessary. The wisdom
|
|
mechanism can actually save and reload many plans at once, not just
|
|
one.
|
|
<span id="index-FFTW_005fMEASURE-1"></span>
|
|
<span id="index-FFTW_005fPATIENT-1"></span>
|
|
<span id="index-FFTW_005fEXHAUSTIVE"></span>
|
|
<span id="index-FFTW_005fESTIMATE-1"></span>
|
|
</p>
|
|
|
|
<p>Whenever you create a plan, the FFTW planner accumulates wisdom, which
|
|
is information sufficient to reconstruct the plan. After planning,
|
|
you can save this information to disk by means of the function:
|
|
</p><div class="example">
|
|
<pre class="example">int fftw_export_wisdom_to_filename(const char *filename);
|
|
</pre></div>
|
|
<span id="index-fftw_005fexport_005fwisdom_005fto_005ffilename"></span>
|
|
<p>(This function returns non-zero on success.)
|
|
</p>
|
|
<p>The next time you run the program, you can restore the wisdom with
|
|
<code>fftw_import_wisdom_from_filename</code> (which also returns non-zero on success),
|
|
and then recreate the plan using the same flags as before.
|
|
</p><div class="example">
|
|
<pre class="example">int fftw_import_wisdom_from_filename(const char *filename);
|
|
</pre></div>
|
|
<span id="index-fftw_005fimport_005fwisdom_005ffrom_005ffilename"></span>
|
|
|
|
<p>Wisdom is automatically used for any size to which it is applicable, as
|
|
long as the planner flags are not more “patient” than those with which
|
|
the wisdom was created. For example, wisdom created with
|
|
<code>FFTW_MEASURE</code> can be used if you later plan with
|
|
<code>FFTW_ESTIMATE</code> or <code>FFTW_MEASURE</code>, but not with
|
|
<code>FFTW_PATIENT</code>.
|
|
</p>
|
|
<p>The <code>wisdom</code> is cumulative, and is stored in a global, private
|
|
data structure managed internally by FFTW. The storage space required
|
|
is minimal, proportional to the logarithm of the sizes the wisdom was
|
|
generated from. If memory usage is a concern, however, the wisdom can
|
|
be forgotten and its associated memory freed by calling:
|
|
</p><div class="example">
|
|
<pre class="example">void fftw_forget_wisdom(void);
|
|
</pre></div>
|
|
<span id="index-fftw_005fforget_005fwisdom"></span>
|
|
|
|
<p>Wisdom can be exported to a file, a string, or any other medium.
|
|
For details, see <a href="Wisdom.html">Wisdom</a>.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Caveats-in-Using-Wisdom.html" accesskey="n" rel="next">Caveats in Using Wisdom</a>, Previous: <a href="Multi_002ddimensional-Array-Format.html" accesskey="p" rel="prev">Multi-dimensional Array Format</a>, Up: <a href="Other-Important-Topics.html" accesskey="u" rel="up">Other Important Topics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|