Mercurial > hg > sv-dependency-builds
diff src/fftw-3.3.3/doc/html/Advanced-Complex-DFTs.html @ 10:37bf6b4a2645
Add FFTW3
| author | Chris Cannam |
|---|---|
| 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/Advanced-Complex-DFTs.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,149 @@ +<html lang="en"> +<head> +<title>Advanced Complex DFTs - 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="Advanced-Interface.html#Advanced-Interface" title="Advanced Interface"> +<link rel="prev" href="Advanced-Interface.html#Advanced-Interface" title="Advanced Interface"> +<link rel="next" href="Advanced-Real_002ddata-DFTs.html#Advanced-Real_002ddata-DFTs" title="Advanced 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="Advanced-Complex-DFTs"></a> +<p> +Next: <a rel="next" accesskey="n" href="Advanced-Real_002ddata-DFTs.html#Advanced-Real_002ddata-DFTs">Advanced Real-data DFTs</a>, +Previous: <a rel="previous" accesskey="p" href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a>, +Up: <a rel="up" accesskey="u" href="Advanced-Interface.html#Advanced-Interface">Advanced Interface</a> +<hr> +</div> + +<h4 class="subsection">4.4.1 Advanced Complex DFTs</h4> + +<pre class="example"> fftw_plan fftw_plan_many_dft(int rank, const int *n, int howmany, + fftw_complex *in, const int *inembed, + int istride, int idist, + fftw_complex *out, const int *onembed, + int ostride, int odist, + int sign, unsigned flags); +</pre> + <p><a name="index-fftw_005fplan_005fmany_005fdft-232"></a> +This routine plans multiple multidimensional complex DFTs, and it +extends the <code>fftw_plan_dft</code> routine (see <a href="Complex-DFTs.html#Complex-DFTs">Complex DFTs</a>) to +compute <code>howmany</code> transforms, each having rank <code>rank</code> and size +<code>n</code>. In addition, the transform data need not be contiguous, but +it may be laid out in memory with an arbitrary stride. To account for +these possibilities, <code>fftw_plan_many_dft</code> adds the new parameters +<code>howmany</code>, {<code>i</code>,<code>o</code>}<code>nembed</code>, +{<code>i</code>,<code>o</code>}<code>stride</code>, and +{<code>i</code>,<code>o</code>}<code>dist</code>. The FFTW basic interface +(see <a href="Complex-DFTs.html#Complex-DFTs">Complex DFTs</a>) provides routines specialized for ranks 1, 2, +and 3, but the advanced interface handles only the general-rank +case. + + <p><code>howmany</code> is the number of transforms to compute. The resulting +plan computes <code>howmany</code> transforms, where the input of the +<code>k</code>-th transform is at location <code>in+k*idist</code> (in C pointer +arithmetic), and its output is at location <code>out+k*odist</code>. Plans +obtained in this way can often be faster than calling FFTW multiple +times for the individual transforms. The basic <code>fftw_plan_dft</code> +interface corresponds to <code>howmany=1</code> (in which case the <code>dist</code> +parameters are ignored). +<a name="index-howmany-parameter-233"></a><a name="index-dist-234"></a> + + <p>Each of the <code>howmany</code> transforms has rank <code>rank</code> and size +<code>n</code>, as in the basic interface. In addition, the advanced +interface allows the input and output arrays of each transform to be +row-major subarrays of larger rank-<code>rank</code> arrays, described by +<code>inembed</code> and <code>onembed</code> parameters, respectively. +{<code>i</code>,<code>o</code>}<code>nembed</code> must be arrays of length <code>rank</code>, +and <code>n</code> should be elementwise less than or equal to +{<code>i</code>,<code>o</code>}<code>nembed</code>. Passing <code>NULL</code> for an +<code>nembed</code> parameter is equivalent to passing <code>n</code> (i.e. same +physical and logical dimensions, as in the basic interface.) + + <p>The <code>stride</code> parameters indicate that the <code>j</code>-th element of +the input or output arrays is located at <code>j*istride</code> or +<code>j*ostride</code>, respectively. (For a multi-dimensional array, +<code>j</code> is the ordinary row-major index.) When combined with the +<code>k</code>-th transform in a <code>howmany</code> loop, from above, this means +that the (<code>j</code>,<code>k</code>)-th element is at <code>j*stride+k*dist</code>. +(The basic <code>fftw_plan_dft</code> interface corresponds to a stride of 1.) +<a name="index-stride-235"></a> + + <p>For in-place transforms, the input and output <code>stride</code> and +<code>dist</code> parameters should be the same; otherwise, the planner may +return <code>NULL</code>. + + <p>Arrays <code>n</code>, <code>inembed</code>, and <code>onembed</code> are not used after +this function returns. You can safely free or reuse them. + + <p><strong>Examples</strong>: +One transform of one 5 by 6 array contiguous in memory: +<pre class="example"> int rank = 2; + int n[] = {5, 6}; + int howmany = 1; + int idist = odist = 0; /* unused because howmany = 1 */ + int istride = ostride = 1; /* array is contiguous in memory */ + int *inembed = n, *onembed = n; +</pre> + <p>Transform of three 5 by 6 arrays, each contiguous in memory, +stored in memory one after another: +<pre class="example"> int rank = 2; + int n[] = {5, 6}; + int howmany = 3; + int idist = odist = n[0]*n[1]; /* = 30, the distance in memory + between the first element + of the first array and the + first element of the second array */ + int istride = ostride = 1; /* array is contiguous in memory */ + int *inembed = n, *onembed = n; +</pre> + <p>Transform each column of a 2d array with 10 rows and 3 columns: +<pre class="example"> int rank = 1; /* not 2: we are computing 1d transforms */ + int n[] = {10}; /* 1d transforms of length 10 */ + int howmany = 3; + int idist = odist = 1; + int istride = ostride = 3; /* distance between two elements in + the same column */ + int *inembed = n, *onembed = n; +</pre> + <!-- =========> --> + </body></html> +