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diff src/fftw-3.3.3/doc/html/Guru-vector-and-transform-sizes.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/Guru-vector-and-transform-sizes.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,116 @@ +<html lang="en"> +<head> +<title>Guru vector and transform sizes - 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="Guru-Interface.html#Guru-Interface" title="Guru Interface"> +<link rel="prev" href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays" title="Interleaved and split arrays"> +<link rel="next" href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" title="Guru Complex 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="Guru-vector-and-transform-sizes"></a> +<p> +Next: <a rel="next" accesskey="n" href="Guru-Complex-DFTs.html#Guru-Complex-DFTs">Guru Complex DFTs</a>, +Previous: <a rel="previous" accesskey="p" href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays">Interleaved and split arrays</a>, +Up: <a rel="up" accesskey="u" href="Guru-Interface.html#Guru-Interface">Guru Interface</a> +<hr> +</div> + +<h4 class="subsection">4.5.2 Guru vector and transform sizes</h4> + +<p>The guru interface introduces one basic new data structure, +<code>fftw_iodim</code>, that is used to specify sizes and strides for +multi-dimensional transforms and vectors: + +<pre class="example"> typedef struct { + int n; + int is; + int os; + } fftw_iodim; +</pre> + <p><a name="index-fftw_005fiodim-243"></a> +Here, <code>n</code> is the size of the dimension, and <code>is</code> and <code>os</code> +are the strides of that dimension for the input and output arrays. (The +stride is the separation of consecutive elements along this dimension.) + + <p>The meaning of the stride parameter depends on the type of the array +that the stride refers to. <em>If the array is interleaved complex, +strides are expressed in units of complex numbers +(</em><code>fftw_complex</code><em>). If the array is split complex or real, strides +are expressed in units of real numbers (</em><code>double</code><em>).</em> This +convention is consistent with the usual pointer arithmetic in the C +language. An interleaved array is denoted by a pointer <code>p</code> to +<code>fftw_complex</code>, so that <code>p+1</code> points to the next complex +number. Split arrays are denoted by pointers to <code>double</code>, in +which case pointer arithmetic operates in units of +<code>sizeof(double)</code>. +<a name="index-stride-244"></a> + + <p>The guru planner interfaces all take a (<code>rank</code>, <code>dims[rank]</code>) +pair describing the transform size, and a (<code>howmany_rank</code>, +<code>howmany_dims[howmany_rank]</code>) pair describing the “vector” size (a +multi-dimensional loop of transforms to perform), where <code>dims</code> and +<code>howmany_dims</code> are arrays of <code>fftw_iodim</code>. + + <p>For example, the <code>howmany</code> parameter in the advanced complex-DFT +interface corresponds to <code>howmany_rank</code> = 1, +<code>howmany_dims[0].n</code> = <code>howmany</code>, <code>howmany_dims[0].is</code> = +<code>idist</code>, and <code>howmany_dims[0].os</code> = <code>odist</code>. +<a name="index-howmany-loop-245"></a><a name="index-dist-246"></a>(To compute a single transform, you can just use <code>howmany_rank</code> = 0.) + + <p>A row-major multidimensional array with dimensions <code>n[rank]</code> +(see <a href="Row_002dmajor-Format.html#Row_002dmajor-Format">Row-major Format</a>) corresponds to <code>dims[i].n</code> = +<code>n[i]</code> and the recurrence <code>dims[i].is</code> = <code>n[i+1] * +dims[i+1].is</code> (similarly for <code>os</code>). The stride of the last +(<code>i=rank-1</code>) dimension is the overall stride of the array. +e.g. to be equivalent to the advanced complex-DFT interface, you would +have <code>dims[rank-1].is</code> = <code>istride</code> and +<code>dims[rank-1].os</code> = <code>ostride</code>. +<a name="index-row_002dmajor-247"></a> + + <p>In general, we only guarantee FFTW to return a non-<code>NULL</code> plan if +the vector and transform dimensions correspond to a set of distinct +indices, and for in-place transforms the input/output strides should +be the same. + +<!-- =========> --> + </body></html> +