Mercurial > hg > sv-dependency-builds
diff src/fftw-3.3.5/doc/html/Row_002dmajor-Format.html @ 42:2cd0e3b3e1fd
Current fftw source
| author | Chris Cannam |
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| date | Tue, 18 Oct 2016 13:40:26 +0100 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.5/doc/html/Row_002dmajor-Format.html Tue Oct 18 13:40:26 2016 +0100 @@ -0,0 +1,116 @@ +<!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 3.3.5, 30 July 2016). + +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 5.2, http://www.gnu.org/software/texinfo/ --> +<head> +<title>FFTW 3.3.5: Row-major Format</title> + +<meta name="description" content="FFTW 3.3.5: Row-major Format"> +<meta name="keywords" content="FFTW 3.3.5: Row-major Format"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="up" title="Multi-dimensional Array Format"> +<link href="Column_002dmajor-Format.html#Column_002dmajor-Format" rel="next" title="Column-major Format"> +<link href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" rel="prev" title="Multi-dimensional Array Format"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {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} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Row_002dmajor-Format"></a> +<div class="header"> +<p> +Next: <a href="Column_002dmajor-Format.html#Column_002dmajor-Format" accesskey="n" rel="next">Column-major Format</a>, Previous: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="p" rel="prev">Multi-dimensional Array Format</a>, Up: <a href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" accesskey="u" rel="up">Multi-dimensional Array Format</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Row_002dmajor-Format-1"></a> +<h4 class="subsection">3.2.1 Row-major Format</h4> +<a name="index-row_002dmajor"></a> + +<p>The multi-dimensional arrays passed to <code>fftw_plan_dft</code> etcetera +are expected to be stored as a single contiguous block in +<em>row-major</em> order (sometimes called “C order”). Basically, this +means that as you step through adjacent memory locations, the first +dimension’s index varies most slowly and the last dimension’s index +varies most quickly. +</p> +<p>To be more explicit, let us consider an array of rank <em>d</em> whose +dimensions are n<sub>0</sub> × n<sub>1</sub> × n<sub>2</sub> × … × n<sub>d-1</sub>. Now, we specify a location in the array by a +sequence of <em>d</em> (zero-based) indices, one for each dimension: +(i<sub>0</sub>, i<sub>1</sub>, i<sub>2</sub>,..., i<sub>d-1</sub>).If the array is stored in row-major +order, then this element is located at the position +i<sub>d-1</sub> + n<sub>d-1</sub> * (i<sub>d-2</sub> + n<sub>d-2</sub> * (... + n<sub>1</sub> * i<sub>0</sub>)).</p> +<p>Note that, for the ordinary complex DFT, each element of the array +must be of type <code>fftw_complex</code>; i.e. a (real, imaginary) pair of +(double-precision) numbers. +</p> +<p>In the advanced FFTW interface, the physical dimensions <em>n</em> from +which the indices are computed can be different from (larger than) +the logical dimensions of the transform to be computed, in order to +transform a subset of a larger array. +<a name="index-advanced-interface-2"></a> +Note also that, in the advanced interface, the expression above is +multiplied by a <em>stride</em> to get the actual array index—this is +useful in situations where each element of the multi-dimensional array +is actually a data structure (or another array), and you just want to +transform a single field. In the basic interface, however, the stride +is 1. +<a name="index-stride"></a> +</p> + + + +</body> +</html>