|
Chris@10
|
1 <html lang="en">
|
|
Chris@10
|
2 <head>
|
|
Chris@10
|
3 <title>Guru vector and transform sizes - FFTW 3.3.3</title>
|
|
Chris@10
|
4 <meta http-equiv="Content-Type" content="text/html">
|
|
Chris@10
|
5 <meta name="description" content="FFTW 3.3.3">
|
|
Chris@10
|
6 <meta name="generator" content="makeinfo 4.13">
|
|
Chris@10
|
7 <link title="Top" rel="start" href="index.html#Top">
|
|
Chris@10
|
8 <link rel="up" href="Guru-Interface.html#Guru-Interface" title="Guru Interface">
|
|
Chris@10
|
9 <link rel="prev" href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays" title="Interleaved and split arrays">
|
|
Chris@10
|
10 <link rel="next" href="Guru-Complex-DFTs.html#Guru-Complex-DFTs" title="Guru Complex DFTs">
|
|
Chris@10
|
11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
Chris@10
|
12 <!--
|
|
Chris@10
|
13 This manual is for FFTW
|
|
Chris@10
|
14 (version 3.3.3, 25 November 2012).
|
|
Chris@10
|
15
|
|
Chris@10
|
16 Copyright (C) 2003 Matteo Frigo.
|
|
Chris@10
|
17
|
|
Chris@10
|
18 Copyright (C) 2003 Massachusetts Institute of Technology.
|
|
Chris@10
|
19
|
|
Chris@10
|
20 Permission is granted to make and distribute verbatim copies of
|
|
Chris@10
|
21 this manual provided the copyright notice and this permission
|
|
Chris@10
|
22 notice are preserved on all copies.
|
|
Chris@10
|
23
|
|
Chris@10
|
24 Permission is granted to copy and distribute modified versions of
|
|
Chris@10
|
25 this manual under the conditions for verbatim copying, provided
|
|
Chris@10
|
26 that the entire resulting derived work is distributed under the
|
|
Chris@10
|
27 terms of a permission notice identical to this one.
|
|
Chris@10
|
28
|
|
Chris@10
|
29 Permission is granted to copy and distribute translations of this
|
|
Chris@10
|
30 manual into another language, under the above conditions for
|
|
Chris@10
|
31 modified versions, except that this permission notice may be
|
|
Chris@10
|
32 stated in a translation approved by the Free Software Foundation.
|
|
Chris@10
|
33 -->
|
|
Chris@10
|
34 <meta http-equiv="Content-Style-Type" content="text/css">
|
|
Chris@10
|
35 <style type="text/css"><!--
|
|
Chris@10
|
36 pre.display { font-family:inherit }
|
|
Chris@10
|
37 pre.format { font-family:inherit }
|
|
Chris@10
|
38 pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
Chris@10
|
39 pre.smallformat { font-family:inherit; font-size:smaller }
|
|
Chris@10
|
40 pre.smallexample { font-size:smaller }
|
|
Chris@10
|
41 pre.smalllisp { font-size:smaller }
|
|
Chris@10
|
42 span.sc { font-variant:small-caps }
|
|
Chris@10
|
43 span.roman { font-family:serif; font-weight:normal; }
|
|
Chris@10
|
44 span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
Chris@10
|
45 --></style>
|
|
Chris@10
|
46 </head>
|
|
Chris@10
|
47 <body>
|
|
Chris@10
|
48 <div class="node">
|
|
Chris@10
|
49 <a name="Guru-vector-and-transform-sizes"></a>
|
|
Chris@10
|
50 <p>
|
|
Chris@10
|
51 Next: <a rel="next" accesskey="n" href="Guru-Complex-DFTs.html#Guru-Complex-DFTs">Guru Complex DFTs</a>,
|
|
Chris@10
|
52 Previous: <a rel="previous" accesskey="p" href="Interleaved-and-split-arrays.html#Interleaved-and-split-arrays">Interleaved and split arrays</a>,
|
|
Chris@10
|
53 Up: <a rel="up" accesskey="u" href="Guru-Interface.html#Guru-Interface">Guru Interface</a>
|
|
Chris@10
|
54 <hr>
|
|
Chris@10
|
55 </div>
|
|
Chris@10
|
56
|
|
Chris@10
|
57 <h4 class="subsection">4.5.2 Guru vector and transform sizes</h4>
|
|
Chris@10
|
58
|
|
Chris@10
|
59 <p>The guru interface introduces one basic new data structure,
|
|
Chris@10
|
60 <code>fftw_iodim</code>, that is used to specify sizes and strides for
|
|
Chris@10
|
61 multi-dimensional transforms and vectors:
|
|
Chris@10
|
62
|
|
Chris@10
|
63 <pre class="example"> typedef struct {
|
|
Chris@10
|
64 int n;
|
|
Chris@10
|
65 int is;
|
|
Chris@10
|
66 int os;
|
|
Chris@10
|
67 } fftw_iodim;
|
|
Chris@10
|
68 </pre>
|
|
Chris@10
|
69 <p><a name="index-fftw_005fiodim-243"></a>
|
|
Chris@10
|
70 Here, <code>n</code> is the size of the dimension, and <code>is</code> and <code>os</code>
|
|
Chris@10
|
71 are the strides of that dimension for the input and output arrays. (The
|
|
Chris@10
|
72 stride is the separation of consecutive elements along this dimension.)
|
|
Chris@10
|
73
|
|
Chris@10
|
74 <p>The meaning of the stride parameter depends on the type of the array
|
|
Chris@10
|
75 that the stride refers to. <em>If the array is interleaved complex,
|
|
Chris@10
|
76 strides are expressed in units of complex numbers
|
|
Chris@10
|
77 (</em><code>fftw_complex</code><em>). If the array is split complex or real, strides
|
|
Chris@10
|
78 are expressed in units of real numbers (</em><code>double</code><em>).</em> This
|
|
Chris@10
|
79 convention is consistent with the usual pointer arithmetic in the C
|
|
Chris@10
|
80 language. An interleaved array is denoted by a pointer <code>p</code> to
|
|
Chris@10
|
81 <code>fftw_complex</code>, so that <code>p+1</code> points to the next complex
|
|
Chris@10
|
82 number. Split arrays are denoted by pointers to <code>double</code>, in
|
|
Chris@10
|
83 which case pointer arithmetic operates in units of
|
|
Chris@10
|
84 <code>sizeof(double)</code>.
|
|
Chris@10
|
85 <a name="index-stride-244"></a>
|
|
Chris@10
|
86
|
|
Chris@10
|
87 <p>The guru planner interfaces all take a (<code>rank</code>, <code>dims[rank]</code>)
|
|
Chris@10
|
88 pair describing the transform size, and a (<code>howmany_rank</code>,
|
|
Chris@10
|
89 <code>howmany_dims[howmany_rank]</code>) pair describing the “vector” size (a
|
|
Chris@10
|
90 multi-dimensional loop of transforms to perform), where <code>dims</code> and
|
|
Chris@10
|
91 <code>howmany_dims</code> are arrays of <code>fftw_iodim</code>.
|
|
Chris@10
|
92
|
|
Chris@10
|
93 <p>For example, the <code>howmany</code> parameter in the advanced complex-DFT
|
|
Chris@10
|
94 interface corresponds to <code>howmany_rank</code> = 1,
|
|
Chris@10
|
95 <code>howmany_dims[0].n</code> = <code>howmany</code>, <code>howmany_dims[0].is</code> =
|
|
Chris@10
|
96 <code>idist</code>, and <code>howmany_dims[0].os</code> = <code>odist</code>.
|
|
Chris@10
|
97 <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.)
|
|
Chris@10
|
98
|
|
Chris@10
|
99 <p>A row-major multidimensional array with dimensions <code>n[rank]</code>
|
|
Chris@10
|
100 (see <a href="Row_002dmajor-Format.html#Row_002dmajor-Format">Row-major Format</a>) corresponds to <code>dims[i].n</code> =
|
|
Chris@10
|
101 <code>n[i]</code> and the recurrence <code>dims[i].is</code> = <code>n[i+1] *
|
|
Chris@10
|
102 dims[i+1].is</code> (similarly for <code>os</code>). The stride of the last
|
|
Chris@10
|
103 (<code>i=rank-1</code>) dimension is the overall stride of the array.
|
|
Chris@10
|
104 e.g. to be equivalent to the advanced complex-DFT interface, you would
|
|
Chris@10
|
105 have <code>dims[rank-1].is</code> = <code>istride</code> and
|
|
Chris@10
|
106 <code>dims[rank-1].os</code> = <code>ostride</code>.
|
|
Chris@10
|
107 <a name="index-row_002dmajor-247"></a>
|
|
Chris@10
|
108
|
|
Chris@10
|
109 <p>In general, we only guarantee FFTW to return a non-<code>NULL</code> plan if
|
|
Chris@10
|
110 the vector and transform dimensions correspond to a set of distinct
|
|
Chris@10
|
111 indices, and for in-place transforms the input/output strides should
|
|
Chris@10
|
112 be the same.
|
|
Chris@10
|
113
|
|
Chris@10
|
114 <!-- =========> -->
|
|
Chris@10
|
115 </body></html>
|
|
Chris@10
|
116
|
