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30 Octonions, like <a class="link" href="../quaternions.html" title="Chapter 15. Quaternions">quaternions</a>, are a relative
34 Octonions see some use in theoretical physics.
37 In practical terms, an octonion is simply an octuple of real numbers (α,β,γ,δ,ε,ζ,η,θ), which
38 we can write in the form <span class="emphasis"><em><code class="literal">o = α + βi + γj + δk + εe' + ζi' + ηj' + θk'</code></em></span>, where
39 <span class="emphasis"><em><code class="literal">i</code></em></span>, <span class="emphasis"><em><code class="literal">j</code></em></span>
40 and <span class="emphasis"><em><code class="literal">k</code></em></span> are the same objects as for quaternions,
41 and <span class="emphasis"><em><code class="literal">e'</code></em></span>, <span class="emphasis"><em><code class="literal">i'</code></em></span>,
42 <span class="emphasis"><em><code class="literal">j'</code></em></span> and <span class="emphasis"><em><code class="literal">k'</code></em></span>
43 are distinct objects which play essentially the same kind of role as <span class="emphasis"><em><code class="literal">i</code></em></span>
44 (or <span class="emphasis"><em><code class="literal">j</code></em></span> or <span class="emphasis"><em><code class="literal">k</code></em></span>).
47 Addition and a multiplication is defined on the set of octonions, which generalize
48 their quaternionic counterparts. The main novelty this time is that <span class="bold"><strong>the multiplication is not only not commutative, is now not even
49 associative</strong></span> (i.e. there are octonions <span class="emphasis"><em><code class="literal">x</code></em></span>,
50 <span class="emphasis"><em><code class="literal">y</code></em></span> and <span class="emphasis"><em><code class="literal">z</code></em></span>
51 such that <span class="emphasis"><em><code class="literal">x(yz) ≠ (xy)z</code></em></span>). A way of remembering
52 things is by using the following multiplication table:
55 <span class="inlinemediaobject"><img src="../../octonion/graphics/octonion_blurb17.jpeg"></span>
58 Octonions (and their kin) are described in far more details in this other
59 <a href="../../quaternion/TQE.pdf" target="_top">document</a> (with <a href="../../quaternion/TQE_EA.pdf" target="_top">errata
63 Some traditional constructs, such as the exponential, carry over without too
64 much change into the realms of octonions, but other, such as taking a square
65 root, do not (the fact that the exponential has a closed form is a result of
66 the author, but the fact that the exponential exists at all for octonions is
67 known since quite a long time ago).
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72 <td align="right"><div class="copyright-footer">Copyright © 2006-2019 Nikhar
73 Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos,
74 Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan
75 Råde, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg,
76 Daryle Walker and Xiaogang Zhang<p>
77 Distributed under the Boost Software License, Version 1.0. (See accompanying
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