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diff src/fftw-3.3.3/doc/html/Words-of-Wisdom_002dSaving-Plans.html @ 10:37bf6b4a2645
Add FFTW3
| author | Chris Cannam |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Words-of-Wisdom_002dSaving-Plans.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,113 @@ +<html lang="en"> +<head> +<title>Words of Wisdom-Saving Plans - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Other-Important-Topics.html#Other-Important-Topics" title="Other Important Topics"> +<link rel="prev" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" title="Multi-dimensional Array Format"> +<link rel="next" href="Caveats-in-Using-Wisdom.html#Caveats-in-Using-Wisdom" title="Caveats in Using Wisdom"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +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. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="Words-of-Wisdom-Saving-Plans"></a> +<a name="Words-of-Wisdom_002dSaving-Plans"></a> +<p> +Next: <a rel="next" accesskey="n" href="Caveats-in-Using-Wisdom.html#Caveats-in-Using-Wisdom">Caveats in Using Wisdom</a>, +Previous: <a rel="previous" accesskey="p" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>, +Up: <a rel="up" accesskey="u" href="Other-Important-Topics.html#Other-Important-Topics">Other Important Topics</a> +<hr> +</div> + +<h3 class="section">3.3 Words of Wisdom—Saving Plans</h3> + +<p><a name="index-wisdom-124"></a><a name="index-saving-plans-to-disk-125"></a> +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 <dfn>wisdom</dfn>. Here, we describe +this feature at a high level. See <a href="FFTW-Reference.html#FFTW-Reference">FFTW Reference</a>, for a less casual +but more complete discussion of how to use wisdom in FFTW. + + <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. +<a name="index-FFTW_005fMEASURE-126"></a><a name="index-FFTW_005fPATIENT-127"></a><a name="index-FFTW_005fEXHAUSTIVE-128"></a><a name="index-FFTW_005fESTIMATE-129"></a> + + <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: +<pre class="example"> int fftw_export_wisdom_to_filename(const char *filename); +</pre> + <p><a name="index-fftw_005fexport_005fwisdom_005fto_005ffilename-130"></a>(This function returns non-zero on success.) + + <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. +<pre class="example"> int fftw_import_wisdom_from_filename(const char *filename); +</pre> + <p><a name="index-fftw_005fimport_005fwisdom_005ffrom_005ffilename-131"></a> +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>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: +<pre class="example"> void fftw_forget_wisdom(void); +</pre> + <p><a name="index-fftw_005fforget_005fwisdom-132"></a> +Wisdom can be exported to a file, a string, or any other medium. +For details, see <a href="Wisdom.html#Wisdom">Wisdom</a>. + + </body></html> +