SIMPLE
TOOLBOX
Here are simple tools for expressing some of the basic
algebraic properties of octonions, namely the commutator, the associator,
and the two structure constants.
Let A,B,C denote three octonions.
(1) Commutator of A and B is defined as
[ A, B ] := AB - BA { |
= 0 if A and B commute |
not 0 if A and B do not commute. |
|
(2) Associator of A, B, C is defined as
( A, B, C ) := (AB) C - A (BC) { |
= 0 if associative |
not 0 if not associative. |
|
Using the associator the alternative property of
octonions is expressed as
( A, A, B ) = (AA) B - A (AB)
= 0 .
We often work with the basis of octonions. i.e
an octonion, A, may be expressed in terms of the basis, im
, as
A := m=0S7
am im
= a0 i0
+ j=1S7
aj ij
,
where Greek indices represent 0,1,...,7, and Latin
indices represent 1,...,7.
Here, the non-commutative and non-associative properties
of basal elements are expressed, more explicitly, using structure constants,
emnr
,
and emnrs
, respectively. Let im
, and in be
two basal elements of octonions.
(3) Structure constant ( 1st kind, relating to commutators
), emnr ,
is defined via a product of two basal elements,
[ im
, in ] :=
im in
- in im
= 2 e
mnr
ir
.
e mnr
are real numbers which equals 0 only when im
commutes with in
.
(4) Structure constant ( 2nd kind, relating to associators
), emnrs
, is defined via a product of three basal elements,
( im
, in ,
ir )
:= ( im
in )
ir
- im
( in
ir )
= 2 emnrs
is
.
emnrs
are real numbers.
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