octonion
Let be the quaternions over the reals . Apply theCayley-Dickson construction to once, and we obtain an algebra
,variously called Cayley algebra, the octonion algebra, or simply the octonions, over . Specifically the construction is carried out as follows:
- 1.
Form the vector space ; any element of can be written as , where ;
- 2.
Define a binary operation
on called the multiplication in by
where , and is the quaternionic conjugation
of . When , the multiplication is reduced themultiplication in . In addition, the multiplication rule aboveimply the following:
(1) (2) (3) In particular, in the last equation, if , .
- 3.
Define a unary operation on called the octonionicconjugation in by
where .Clearly, the octonionic conjugation is an involution
(http://planetmath.org/Involution2)().
- 4.
Finally, define a unary operation on called the norm in by , where . Write, then
It is not hard to see that iff .
The above four (actually, only the first two suffice) steps makes into an -dimensional algebra over such that isembedded as a subalgebra.
With the last two steps, one can define the inverse of a non-zeroelement by
so that. Since is arbitrary, has no zerodivisors. Upon checking that , the non-associative algebra is turned into a division algebra
.
Since for any , we can define a non-negativereal-valued function on by . This is clearly well-defined and iff. In addition, it is not hard to see that, for any and , , and that satisfies the triangular inequality. This makes into a normeddivision algebra.
Since the multiplication in is noncommutative, isnoncommutative. In fact, if we write ,where are the complex numbers and , then is a basisfor the vector space over . With the introductionof , we quickly check that anti-commute with the non-real basis elements in :
Furthermore, one checks that , so that is not associative.
Since , the set () is abasis for over . A less messy way to represent these basiselements is done the following assignment:
Title | octonion |
---|---|
Canonical name | Octonion |
Date of creation | 2013-03-22 15:21:42 |
Last modified on | 2013-03-22 15:21:42 |
Owner | CWoo (3771) |
Last modified by | CWoo (3771) |
Numerical id | 15 |
Author | CWoo (3771) |
Entry type | Definition |
Classification | msc 17A75 |
Classification | msc 17D05 |
Synonym | Cayley algebra |
Related topic | TheoremsOnSumsOfSquares |
Related topic | DivisionAlgebra |
Defines | octonion algebra |
\\@unrecurse |