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<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Overview</title> <link rel="stylesheet" href="../math.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../index.html" title="Math Toolkit 2.1.0"> <link rel="up" href="../quaternions.html" title="Chapter&#160;9.&#160;Quaternions"> <link rel="prev" href="../quaternions.html" title="Chapter&#160;9.&#160;Quaternions"> <link rel="next" href="quat_header.html" title="Header File"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> <td align="center"><a href="../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../quaternions.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quaternions.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="quat_header.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="math_toolkit.quat_overview"></a><a class="link" href="quat_overview.html" title="Overview">Overview</a> </h2></div></div></div> <p> Quaternions are a relative of complex numbers. </p> <p> Quaternions are in fact part of a small hierarchy of structures built upon the real numbers, which comprise only the set of real numbers (traditionally named <span class="emphasis"><em><span class="bold"><strong>R</strong></span></em></span>), the set of complex numbers (traditionally named <span class="emphasis"><em><span class="bold"><strong>C</strong></span></em></span>), the set of quaternions (traditionally named <span class="emphasis"><em><span class="bold"><strong>H</strong></span></em></span>) and the set of octonions (traditionally named <span class="emphasis"><em><span class="bold"><strong>O</strong></span></em></span>), which possess interesting mathematical properties (chief among which is the fact that they are <span class="emphasis"><em>division algebras</em></span>, <span class="emphasis"><em>i.e.</em></span> where the following property is true: if <span class="emphasis"><em><code class="literal">y</code></em></span> is an element of that algebra and is <span class="bold"><strong>not equal to zero</strong></span>, then <span class="emphasis"><em><code class="literal">yx = yx'</code></em></span>, where <span class="emphasis"><em><code class="literal">x</code></em></span> and <span class="emphasis"><em><code class="literal">x'</code></em></span> denote elements of that algebra, implies that <span class="emphasis"><em><code class="literal">x = x'</code></em></span>). Each member of the hierarchy is a super-set of the former. </p> <p> One of the most important aspects of quaternions is that they provide an efficient way to parameterize rotations in <span class="emphasis"><em><span class="bold"><strong>R<sup>3</sup></strong></span></em></span> (the usual three-dimensional space) and <span class="emphasis"><em><span class="bold"><strong>R<sup>4</sup></strong></span></em></span>. </p> <p> In practical terms, a quaternion is simply a quadruple of real numbers (&#945;,&#946;,&#947;,&#948;), which we can write in the form <span class="emphasis"><em><code class="literal">q = &#945; + &#946;i + &#947;j + &#948;k</code></em></span>, where <span class="emphasis"><em><code class="literal">i</code></em></span> is the same object as for complex numbers, and <span class="emphasis"><em><code class="literal">j</code></em></span> and <span class="emphasis"><em><code class="literal">k</code></em></span> are distinct objects which play essentially the same kind of role as <span class="emphasis"><em><code class="literal">i</code></em></span>. </p> <p> An addition and a multiplication is defined on the set of quaternions, which generalize their real and complex counterparts. The main novelty here is that <span class="bold"><strong>the multiplication is not commutative</strong></span> (i.e. there are quaternions <span class="emphasis"><em><code class="literal">x</code></em></span> and <span class="emphasis"><em><code class="literal">y</code></em></span> such that <span class="emphasis"><em><code class="literal">xy &#8800; yx</code></em></span>). A good mnemotechnical way of remembering things is by using the formula <span class="emphasis"><em><code class="literal">i*i = j*j = k*k = -1</code></em></span>. </p> <p> Quaternions (and their kin) are described in far more details in this other <a href="../../../quaternion/TQE.pdf" target="_top">document</a> (with <a href="../../../quaternion/TQE_EA.pdf" target="_top">errata and addenda</a>). </p> <p> Some traditional constructs, such as the exponential, carry over without too much change into the realms of quaternions, but other, such as taking a square root, do not. </p> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2010, 2012-2014 Nikhar Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert Holin, Bruno Lalande, John Maddock, Johan R&#229;de, Gautam Sewani, Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../quaternions.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quaternions.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="quat_header.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>