Octonion Algebra Is Frobenius In Just One Way
Linear operators over a 8-dimensional vector space representing octonnion algebra
Ref:
We need the Axiom LinearOperator? library.
axiom
)library CARTEN MONAL PROP LOP CALEY
CartesianTensor is now explicitly exposed in frame initial
CartesianTensor will be automatically loaded when needed from
/var/zope2/var/LatexWiki/CARTEN.NRLIB/CARTEN
Monoidal is now explicitly exposed in frame initial
Monoidal will be automatically loaded when needed from
/var/zope2/var/LatexWiki/MONAL.NRLIB/MONAL
Prop is now explicitly exposed in frame initial
Prop will be automatically loaded when needed from
/var/zope2/var/LatexWiki/PROP.NRLIB/PROP
LinearOperator is now explicitly exposed in frame initial
LinearOperator will be automatically loaded when needed from
/var/zope2/var/LatexWiki/LOP.NRLIB/LOP
CaleyDickson is now explicitly exposed in frame initial
CaleyDickson will be automatically loaded when needed from
/var/zope2/var/LatexWiki/CALEY.NRLIB/CALEY
Use the following macros for convenient notation
axiom
-- summation
macro Σ(x,i,n)==reduce(+,[x for i in n])
Type: Void
axiom
-- list
macro Ξ(f,i,n)==[f for i in n]
Type: Void
axiom
-- subscript
macro sb == subscript
Type: Void
𝐋 is the domain of 8-dimensional linear operators over the rational functions ℚ (Expression Integer), i.e. ratio of polynomials with integer coefficients.
axiom
dim:=8
axiom
macro ℒ == List
Type: Void
axiom
macro ℂ == CaleyDickson
Type: Void
axiom
macro ℚ == Expression Integer
Type: Void
axiom
𝐋 := LinearOperator(OVAR ['0,'1,'2,'3,'4,'5,'6,'7], ℚ)
Type: Type
axiom
𝐞:ℒ 𝐋 := basisOut()
Type: List(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
axiom
𝐝:ℒ 𝐋 := basisIn()
Type: List(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
axiom
I:𝐋:=[1]; -- identity for composition
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
X:𝐋:=[2,1]; -- twist
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
Now generate structure constants for Octonion Algebra
The basis consists of the real and imaginary units. We use quaternion multiplication to form the "multiplication table" as a matrix. Then the structure constants can be obtained by dividing each matrix entry by the list of basis vectors.
Split-complex, co-quaternions and split-octonions can be specified by Caley-Dickson parameters
axiom
--q0:=sb('q,[0])
q0:=1 -- not split-complex
axiom
--q1:=sb('q,[1])
q1:=1 -- not co-quaternion
axiom
q2:=sb('q,[2])
Type: Symbol
axiom
--q2:=1 -- split-octonion
QQ := ℂ(ℂ(ℂ(ℚ,'i,q0),'j,q1),'k,q2);
Type: Type
Basis: Each B.i is a octonion number
axiom
B:ℒ QQ := map(x +-> hyper x,1$SQMATRIX(dim,ℚ)::ℒ ℒ ℚ)
Type: List(CaleyDickson
?(CaleyDickson
?(CaleyDickson
?(Expression(Integer),
i,
1),
j,
1),
k,
*01q(2)))
axiom
-- Multiplication table:
M:Matrix QQ := matrix Ξ(Ξ(B.i*B.j, i,1..dim), j,1..dim)
Type: Matrix(CaleyDickson
?(CaleyDickson
?(CaleyDickson
?(Expression(Integer),
i,
1),
j,
1),
k,
*01q(2)))
axiom
-- Function to divide the matrix entries by a basis element
S(y) == map(x +-> real real real(x/y),M)
Type: Void
axiom
-- The result is a nested list
ѕ :=map(S,B)::ℒ ℒ ℒ ℚ;
axiom
Compiling function S with type CaleyDickson(CaleyDickson(
CaleyDickson(Expression(Integer),i,1),j,1),k,*01q(2)) -> Matrix(
Expression(Integer))
Type: List(List(List(Expression(Integer))))
axiom
-- structure constants form a tensor operator
Y := Σ(Σ(Σ(ѕ(i)(k)(j)*𝐞.i*𝐝.j*𝐝.k, i,1..dim), j,1..dim), k,1..dim)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
arity Y
Type: Prop(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
axiom
matrix Ξ(Ξ((𝐞.i*𝐞.j)/Y, i,1..dim), j,1..dim)
Type: Matrix(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
A scalar product is denoted by the (2,0)-tensor
axiom
U:=Σ(Σ(script('u,[[],[i,j]])*𝐝.i*𝐝.j, i,1..dim), j,1..dim)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
Definition 1
We say that the scalar product is associative if the tensor
equation holds:
Y = Y
U U
In other words, if the (3,0)-tensor:
(three-point function) is zero.
Using the LinearOperator? domain in Axiom and some carefully chosen symbols we can easily enter expressions that are both readable and interpreted by Axiom as "graphical calculus" diagrams describing complex products and compositions of linear operators.
axiom
ω:𝐋 :=(Y*I)/U - (I*Y)/U;
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
Definition 2
An algebra with a non-degenerate associative scalar product
is called a [Frobenius Algebra]?.
We may consider the problem where multiplication Y is given,
and look for all associative scalar products
This problem can be solved using linear algebra.
axiom
)expose MCALCFN
MultiVariableCalculusFunctions is now explicitly exposed in frame
initial
J := jacobian(ravel ω,concat map(variables,ravel U)::ℒ Symbol);
Type: Matrix(Expression(Integer))
axiom
u := transpose matrix [concat map(variables,ravel U)::ℒ Symbol];
Type: Matrix(Polynomial(Integer))
axiom
J::OutputForm * u::OutputForm = 0
Type: Equation(OutputForm
?)
axiom
nrows(J),ncols(J)
Type: Tuple(PositiveInteger
?)
The matrix J
transforms the coefficients of the tensor
into coefficients of the tensor . We are looking for
the general linear family of tensors such that
J
transforms into for any such .
If the null space of the J
matrix is not empty we can use
the basis to find all non-trivial solutions for U:
axiom
Ñ:=nullSpace(J);
Type: List(Vector(Expression(Integer)))
axiom
ℰ:=map((x,y)+->x=y, concat
map(variables,ravel U), entries Σ(sb('p,[i])*Ñ.i, i,1..#Ñ) )
Type: List(Equation(Expression(Integer)))
This defines a family of Frobenius algebras:
axiom
zero? eval(ω,ℰ)
Type: Boolean
The pairing is necessarily diagonal!
axiom
Ų:𝐋 := eval(U,ℰ)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
matrix Ξ(Ξ((𝐞.i 𝐞.j)/Ų, i,1..dim), j,1..dim)
Type: Matrix(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
The scalar product must be non-degenerate:
axiom
Ů:=determinant Ξ(Ξ(retract((𝐞.i * 𝐞.j)/Ų), j,1..dim), i,1..dim)
Type: Expression(Integer)
axiom
factor Ů
Type: Factored(Expression(Integer))
Definition 3
Co-pairing
Solve the [Snake Relation]? as a system of linear equations.
axiom
Um:=matrix Ξ(Ξ((𝐞.i*𝐞.j)/Ų, i,1..dim), j,1..dim)
Type: Matrix(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
axiom
mU:=transpose inverse map(retract,Um)
Type: Matrix(Expression(Integer))
axiom
Ω:=Σ(Σ(mU(i,j)*(𝐞.i*𝐞.j), i,1..dim), j,1..dim)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
matrix Ξ(Ξ(Ω/(𝐝.i*𝐝.j), i,1..dim), j,1..dim)
Type: Matrix(LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer)))
Check "dimension" and the snake relations.
axiom
d:𝐋:=
Ω /
X /
Ų
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
test
( I Ω ) /
( Ų I ) = I
Type: Boolean
axiom
test
( Ω I ) /
( I Ų ) = I
Type: Boolean
Definition 4
Co-algebra
Compute the "three-point" function and use it to define co-multiplication.
axiom
W:=(Y,I)/Ų
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
λ:=(Ω,I,Ω)/(I,W,I)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
test
( I Ω ) /
( Y I ) = λ
Type: Boolean
axiom
test
( Ω I ) /
( I Y ) = λ
Type: Boolean
Frobenius Condition
Octonion algebra fails the Frobenius Condition!
axiom
Χ :=
Y /
λ
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
Χr := (λ,I)/(I,Y)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
test(Χr = Χ )
Type: Boolean
axiom
Χl := (I,λ)/(Y,I);
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
test( Χl = Χ )
Type: Boolean
axiom
test( Χr = Χl )
Type: Boolean
Perhaps this is not too surprising since Octonion algebra is
non-associative. Nevertheless Octonions are "Frobenius" in a more
general sense because there is a non-degenerate associative
pairing.
i = Unit of the algebra
axiom
i:=𝐞.1
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
test
i /
λ = Ω
Type: Boolean
Handle
axiom
H:𝐋 :=
λ /
X /
Y
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
Definition 5
Co-unit
i
U
axiom
ι:𝐋:=
( i I ) /
( Ų )
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
Y=U
ι
axiom
test
Y /
ι = Ų
Type: Boolean
For example:
axiom
ex1:=[q[2]=1,p[1]=1]
Type: List(Equation(Polynomial(Integer)))
axiom
Ų0:𝐋 :=eval(Ų,ex1)
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
Ω0:𝐋 :=eval(Ω,ex1)$𝐋
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
λ0:𝐋 :=eval(λ,ex1)$𝐋
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))
axiom
H0:𝐋 :=eval(H,ex1)$𝐋
Type: LinearOperator
?(OrderedVariableList
?([0,
1,
2,
3,
4,
5,
6,
7]),
Expression(Integer))