Mercurial > hg > js-dsp-test

annotate fft/fftw/fftw-3.3.4/doc/html/Guru-vector-and-transform-sizes.html @ 40:223f770b5341 kissfft-double tip

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Try a double-precision kissfft
author Chris Cannam
date Wed, 07 Sep 2016 10:40:32 +0100
parents 26056e866c29
children
rev   line source
Chris@19 1 <html lang="en">
Chris@19 2 <head>
Chris@19 3 <title>Guru vector and transform sizes - FFTW 3.3.4</title>
Chris@19 4 <meta http-equiv="Content-Type" content="text/html">
Chris@19 5 <meta name="description" content="FFTW 3.3.4">
Chris@19 6 <meta name="generator" content="makeinfo 4.13">
Chris@19 7 <link title="Top" rel="start" href="index.html#Top">
Chris@19 8 <link rel="up" href="Guru-Interface.html#Guru-Interface" title="Guru Interface">
Chris@19 9 <link rel="prev" href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays" title="Interleaved and split arrays">
Chris@19 10 <link rel="next" href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" title="Guru Complex DFTs">
Chris@19 11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
Chris@19 12 <!--
Chris@19 13 This manual is for FFTW
Chris@19 14 (version 3.3.4, 20 September 2013).
Chris@19 15
Chris@19 16 Copyright (C) 2003 Matteo Frigo.
Chris@19 17
Chris@19 18 Copyright (C) 2003 Massachusetts Institute of Technology.
Chris@19 19
Chris@19 20 Permission is granted to make and distribute verbatim copies of
Chris@19 21 this manual provided the copyright notice and this permission
Chris@19 22 notice are preserved on all copies.
Chris@19 23
Chris@19 24 Permission is granted to copy and distribute modified versions of
Chris@19 25 this manual under the conditions for verbatim copying, provided
Chris@19 26 that the entire resulting derived work is distributed under the
Chris@19 27 terms of a permission notice identical to this one.
Chris@19 28
Chris@19 29 Permission is granted to copy and distribute translations of this
Chris@19 30 manual into another language, under the above conditions for
Chris@19 31 modified versions, except that this permission notice may be
Chris@19 32 stated in a translation approved by the Free Software Foundation.
Chris@19 33 -->
Chris@19 34 <meta http-equiv="Content-Style-Type" content="text/css">
Chris@19 35 <style type="text/css"><!--
Chris@19 36 pre.display { font-family:inherit }
Chris@19 37 pre.format { font-family:inherit }
Chris@19 38 pre.smalldisplay { font-family:inherit; font-size:smaller }
Chris@19 39 pre.smallformat { font-family:inherit; font-size:smaller }
Chris@19 40 pre.smallexample { font-size:smaller }
Chris@19 41 pre.smalllisp { font-size:smaller }
Chris@19 42 span.sc { font-variant:small-caps }
Chris@19 43 span.roman { font-family:serif; font-weight:normal; }
Chris@19 44 span.sansserif { font-family:sans-serif; font-weight:normal; }
Chris@19 45 --></style>
Chris@19 46 </head>
Chris@19 47 <body>
Chris@19 48 <div class="node">
Chris@19 49 <a name="Guru-vector-and-transform-sizes"></a>
Chris@19 50 <p>
Chris@19 51 Next:&nbsp;<a rel="next" accesskey="n" href="Guru-Complex-DFTs.html#Guru-Complex-DFTs">Guru Complex DFTs</a>,
Chris@19 52 Previous:&nbsp;<a rel="previous" accesskey="p" href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays">Interleaved and split arrays</a>,
Chris@19 53 Up:&nbsp;<a rel="up" accesskey="u" href="Guru-Interface.html#Guru-Interface">Guru Interface</a>
Chris@19 54 <hr>
Chris@19 55 </div>
Chris@19 56
Chris@19 57 <h4 class="subsection">4.5.2 Guru vector and transform sizes</h4>
Chris@19 58
Chris@19 59 <p>The guru interface introduces one basic new data structure,
Chris@19 60 <code>fftw_iodim</code>, that is used to specify sizes and strides for
Chris@19 61 multi-dimensional transforms and vectors:
Chris@19 62
Chris@19 63 <pre class="example"> typedef struct {
Chris@19 64 int n;
Chris@19 65 int is;
Chris@19 66 int os;
Chris@19 67 } fftw_iodim;
Chris@19 68 </pre>
Chris@19 69 <p><a name="index-fftw_005fiodim-245"></a>
Chris@19 70 Here, <code>n</code> is the size of the dimension, and <code>is</code> and <code>os</code>
Chris@19 71 are the strides of that dimension for the input and output arrays. (The
Chris@19 72 stride is the separation of consecutive elements along this dimension.)
Chris@19 73
Chris@19 74 <p>The meaning of the stride parameter depends on the type of the array
Chris@19 75 that the stride refers to. <em>If the array is interleaved complex,
Chris@19 76 strides are expressed in units of complex numbers
Chris@19 77 (</em><code>fftw_complex</code><em>). If the array is split complex or real, strides
Chris@19 78 are expressed in units of real numbers (</em><code>double</code><em>).</em> This
Chris@19 79 convention is consistent with the usual pointer arithmetic in the C
Chris@19 80 language. An interleaved array is denoted by a pointer <code>p</code> to
Chris@19 81 <code>fftw_complex</code>, so that <code>p+1</code> points to the next complex
Chris@19 82 number. Split arrays are denoted by pointers to <code>double</code>, in
Chris@19 83 which case pointer arithmetic operates in units of
Chris@19 84 <code>sizeof(double)</code>.
Chris@19 85 <a name="index-stride-246"></a>
Chris@19 86
Chris@19 87 <p>The guru planner interfaces all take a (<code>rank</code>, <code>dims[rank]</code>)
Chris@19 88 pair describing the transform size, and a (<code>howmany_rank</code>,
Chris@19 89 <code>howmany_dims[howmany_rank]</code>) pair describing the &ldquo;vector&rdquo; size (a
Chris@19 90 multi-dimensional loop of transforms to perform), where <code>dims</code> and
Chris@19 91 <code>howmany_dims</code> are arrays of <code>fftw_iodim</code>.
Chris@19 92
Chris@19 93 <p>For example, the <code>howmany</code> parameter in the advanced complex-DFT
Chris@19 94 interface corresponds to <code>howmany_rank</code> = 1,
Chris@19 95 <code>howmany_dims[0].n</code> = <code>howmany</code>, <code>howmany_dims[0].is</code> =
Chris@19 96 <code>idist</code>, and <code>howmany_dims[0].os</code> = <code>odist</code>.
Chris@19 97 <a name="index-howmany-loop-247"></a><a name="index-dist-248"></a>(To compute a single transform, you can just use <code>howmany_rank</code> = 0.)
Chris@19 98
Chris@19 99 <p>A row-major multidimensional array with dimensions <code>n[rank]</code>
Chris@19 100 (see <a href="Row_002dmajor-Format.html#Row_002dmajor-Format">Row-major Format</a>) corresponds to <code>dims[i].n</code> =
Chris@19 101 <code>n[i]</code> and the recurrence <code>dims[i].is</code> = <code>n[i+1] *
Chris@19 102 dims[i+1].is</code> (similarly for <code>os</code>). The stride of the last
Chris@19 103 (<code>i=rank-1</code>) dimension is the overall stride of the array.
Chris@19 104 e.g. to be equivalent to the advanced complex-DFT interface, you would
Chris@19 105 have <code>dims[rank-1].is</code> = <code>istride</code> and
Chris@19 106 <code>dims[rank-1].os</code> = <code>ostride</code>.
Chris@19 107 <a name="index-row_002dmajor-249"></a>
Chris@19 108
Chris@19 109 <p>In general, we only guarantee FFTW to return a non-<code>NULL</code> plan if
Chris@19 110 the vector and transform dimensions correspond to a set of distinct
Chris@19 111 indices, and for in-place transforms the input/output strides should
Chris@19 112 be the same.
Chris@19 113
Chris@19 114 <!-- =========> -->
Chris@19 115 </body></html>
Chris@19 116