mirror of
https://github.com/tildearrow/furnace.git
synced 2024-11-01 18:42:40 +00:00
142 lines
6.7 KiB
HTML
142 lines
6.7 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- This manual is for FFTW
|
|
(version 3.3.10, 10 December 2020).
|
|
|
|
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. -->
|
|
<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>Guru vector and transform sizes (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Guru vector and transform sizes (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Guru vector and transform sizes (FFTW 3.3.10)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Guru-Interface.html" rel="up" title="Guru Interface">
|
|
<link href="Guru-Complex-DFTs.html" rel="next" title="Guru Complex DFTs">
|
|
<link href="Interleaved-and-split-arrays.html" rel="prev" title="Interleaved and split arrays">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<span id="Guru-vector-and-transform-sizes"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Guru-Complex-DFTs.html" accesskey="n" rel="next">Guru Complex DFTs</a>, Previous: <a href="Interleaved-and-split-arrays.html" accesskey="p" rel="prev">Interleaved and split arrays</a>, Up: <a href="Guru-Interface.html" accesskey="u" rel="up">Guru Interface</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<span id="Guru-vector-and-transform-sizes-1"></span><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:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">typedef struct {
|
|
int n;
|
|
int is;
|
|
int os;
|
|
} fftw_iodim;
|
|
</pre></div>
|
|
<span id="index-fftw_005fiodim"></span>
|
|
|
|
<p>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>
|
|
<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
|
|
(<code>fftw_complex</code>). If the array is split complex or real, strides
|
|
are expressed in units of real numbers (<code>double</code>).</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>.
|
|
<span id="index-stride-2"></span>
|
|
</p>
|
|
|
|
<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>. Each <code>n</code> field must
|
|
be positive for <code>dims</code> and nonnegative for <code>howmany_dims</code>, while both
|
|
<code>rank</code> and <code>howmany_rank</code> must be nonnegative.
|
|
</p>
|
|
<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>.
|
|
<span id="index-howmany-loop"></span>
|
|
<span id="index-dist-1"></span>
|
|
(To compute a single transform, you can just use <code>howmany_rank</code> = 0.)
|
|
</p>
|
|
|
|
<p>A row-major multidimensional array with dimensions <code>n[rank]</code>
|
|
(see <a href="Row_002dmajor-Format.html">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>.
|
|
<span id="index-row_002dmajor-3"></span>
|
|
</p>
|
|
|
|
<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.
|
|
</p>
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Next: <a href="Guru-Complex-DFTs.html" accesskey="n" rel="next">Guru Complex DFTs</a>, Previous: <a href="Interleaved-and-split-arrays.html" accesskey="p" rel="prev">Interleaved and split arrays</a>, Up: <a href="Guru-Interface.html" accesskey="u" rel="up">Guru Interface</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|