Mercurial > hg > sv-dependency-builds
diff src/fftw-3.3.3/doc/html/Planner-Flags.html @ 95:89f5e221ed7b
Add FFTW3
| author | Chris Cannam <cannam@all-day-breakfast.com> |
|---|---|
| date | Wed, 20 Mar 2013 15:35:50 +0000 |
| parents | |
| children |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Planner-Flags.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,170 @@ +<html lang="en"> +<head> +<title>Planner Flags - 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="Basic-Interface.html#Basic-Interface" title="Basic Interface"> +<link rel="prev" href="Complex-DFTs.html#Complex-DFTs" title="Complex DFTs"> +<link rel="next" href="Real_002ddata-DFTs.html#Real_002ddata-DFTs" title="Real-data DFTs"> +<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="Planner-Flags"></a> +<p> +Next: <a rel="next" accesskey="n" href="Real_002ddata-DFTs.html#Real_002ddata-DFTs">Real-data DFTs</a>, +Previous: <a rel="previous" accesskey="p" href="Complex-DFTs.html#Complex-DFTs">Complex DFTs</a>, +Up: <a rel="up" accesskey="u" href="Basic-Interface.html#Basic-Interface">Basic Interface</a> +<hr> +</div> + +<h4 class="subsection">4.3.2 Planner Flags</h4> + +<p>All of the planner routines in FFTW accept an integer <code>flags</code> +argument, which is a bitwise OR (‘<samp><span class="samp">|</span></samp>’) of zero or more of the flag +constants defined below. These flags control the rigor (and time) of +the planning process, and can also impose (or lift) restrictions on the +type of transform algorithm that is employed. + + <p><em>Important:</em> the planner overwrites the input array during +planning unless a saved plan (see <a href="Wisdom.html#Wisdom">Wisdom</a>) is available for that +problem, so you should initialize your input data after creating the +plan. The only exceptions to this are the <code>FFTW_ESTIMATE</code> and +<code>FFTW_WISDOM_ONLY</code> flags, as mentioned below. + + <p>In all cases, if wisdom is available for the given problem that was +created with equal-or-greater planning rigor, then the more rigorous +wisdom is used. For example, in <code>FFTW_ESTIMATE</code> mode any available +wisdom is used, whereas in <code>FFTW_PATIENT</code> mode only wisdom created +in patient or exhaustive mode can be used. See <a href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans">Words of Wisdom-Saving Plans</a>. + +<h5 class="subsubheading">Planning-rigor flags</h5> + + <ul> +<li><a name="index-FFTW_005fESTIMATE-171"></a><code>FFTW_ESTIMATE</code> specifies that, instead of actual measurements of +different algorithms, a simple heuristic is used to pick a (probably +sub-optimal) plan quickly. With this flag, the input/output arrays are +not overwritten during planning. + + <li><a name="index-FFTW_005fMEASURE-172"></a><code>FFTW_MEASURE</code> tells FFTW to find an optimized plan by actually +<em>computing</em> several FFTs and measuring their execution time. +Depending on your machine, this can take some time (often a few +seconds). <code>FFTW_MEASURE</code> is the default planning option. + + <li><a name="index-FFTW_005fPATIENT-173"></a><code>FFTW_PATIENT</code> is like <code>FFTW_MEASURE</code>, but considers a wider +range of algorithms and often produces a “more optimal” plan +(especially for large transforms), but at the expense of several times +longer planning time (especially for large transforms). + + <li><a name="index-FFTW_005fEXHAUSTIVE-174"></a><code>FFTW_EXHAUSTIVE</code> is like <code>FFTW_PATIENT</code>, but considers an +even wider range of algorithms, including many that we think are +unlikely to be fast, to produce the most optimal plan but with a +substantially increased planning time. + + <li><a name="index-FFTW_005fWISDOM_005fONLY-175"></a><code>FFTW_WISDOM_ONLY</code> is a special planning mode in which the plan +is only created if wisdom is available for the given problem, and +otherwise a <code>NULL</code> plan is returned. This can be combined with +other flags, e.g. ‘<samp><span class="samp">FFTW_WISDOM_ONLY | FFTW_PATIENT</span></samp>’ creates a +plan only if wisdom is available that was created in +<code>FFTW_PATIENT</code> or <code>FFTW_EXHAUSTIVE</code> mode. The +<code>FFTW_WISDOM_ONLY</code> flag is intended for users who need to detect +whether wisdom is available; for example, if wisdom is not available +one may wish to allocate new arrays for planning so that user data is +not overwritten. + +</ul> + +<h5 class="subsubheading">Algorithm-restriction flags</h5> + + <ul> +<li><a name="index-FFTW_005fDESTROY_005fINPUT-176"></a><code>FFTW_DESTROY_INPUT</code> specifies that an out-of-place transform is +allowed to <em>overwrite its input</em> array with arbitrary data; this +can sometimes allow more efficient algorithms to be employed. +<a name="index-out_002dof_002dplace-177"></a> +<li><a name="index-FFTW_005fPRESERVE_005fINPUT-178"></a><code>FFTW_PRESERVE_INPUT</code> specifies that an out-of-place transform must +<em>not change its input</em> array. This is ordinarily the +<em>default</em>, except for c2r and hc2r (i.e. complex-to-real) +transforms for which <code>FFTW_DESTROY_INPUT</code> is the default. In the +latter cases, passing <code>FFTW_PRESERVE_INPUT</code> will attempt to use +algorithms that do not destroy the input, at the expense of worse +performance; for multi-dimensional c2r transforms, however, no +input-preserving algorithms are implemented and the planner will return +<code>NULL</code> if one is requested. +<a name="index-c2r-179"></a><a name="index-hc2r-180"></a> +<li><a name="index-FFTW_005fUNALIGNED-181"></a><a name="index-alignment-182"></a><code>FFTW_UNALIGNED</code> specifies that the algorithm may not impose any +unusual alignment requirements on the input/output arrays (i.e. no +SIMD may be used). This flag is normally <em>not necessary</em>, since +the planner automatically detects misaligned arrays. The only use for +this flag is if you want to use the new-array execute interface to +execute a given plan on a different array that may not be aligned like +the original. (Using <code>fftw_malloc</code> makes this flag unnecessary +even then.) + +</ul> + +<h5 class="subsubheading">Limiting planning time</h5> + +<pre class="example"> extern void fftw_set_timelimit(double seconds); +</pre> + <p><a name="index-fftw_005fset_005ftimelimit-183"></a> +This function instructs FFTW to spend at most <code>seconds</code> seconds +(approximately) in the planner. If <code>seconds == +FFTW_NO_TIMELIMIT</code> (the default value, which is negative), then +planning time is unbounded. Otherwise, FFTW plans with a +progressively wider range of algorithms until the the given time limit +is reached or the given range of algorithms is explored, returning the +best available plan. +<a name="index-FFTW_005fNO_005fTIMELIMIT-184"></a> + + <p>For example, specifying <code>FFTW_PATIENT</code> first plans in +<code>FFTW_ESTIMATE</code> mode, then in <code>FFTW_MEASURE</code> mode, then +finally (time permitting) in <code>FFTW_PATIENT</code>. If +<code>FFTW_EXHAUSTIVE</code> is specified instead, the planner will further +progress to <code>FFTW_EXHAUSTIVE</code> mode. + + <p>Note that the <code>seconds</code> argument specifies only a rough limit; in +practice, the planner may use somewhat more time if the time limit is +reached when the planner is in the middle of an operation that cannot +be interrupted. At the very least, the planner will complete planning +in <code>FFTW_ESTIMATE</code> mode (which is thus equivalent to a time limit +of 0). + +<!-- =========> --> + </body></html> +