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Frobenius Algebra, Vector Spaces and Polynomial Ideals

Edit detail for Frobenius Algebra, Vector Spaces and Polynomial Ideals revision 4 of 4

	1 2 3 4
Editor: Bill Page Time: 2022/10/11 16:42:44 GMT+0
Note: fix groebner type

changed:
-groebner(ravel(YC))
-\end{axiom}
groebner(map(x+->x,ravel(YC))$LIST2(EXPR INT,POLY INT))
\end{axiom}

changed:
-groebner(ravel(YA))
-\end{axiom}
groebner(map(x+->x,ravel(YA))$LIST2(EXPR INT,POLY INT))
\end{axiom}

References

Frobenius algebras and 2D topological quantum field theories by Joachim Kock
Especially "Tensor calculus (linear algebra in coordinates)" in section 2.3.31, page 123.

2-d Example

Use LinearOperator (LOP)

fricas

(1) -> )lib CARTEN MONAL PROP LOP

   CartesianTensor is now explicitly exposed in frame initial 
   CartesianTensor will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/CARTEN.NRLIB/CARTEN
   Monoidal is now explicitly exposed in frame initial 
   Monoidal will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/MONAL.NRLIB/MONAL
   Prop is now explicitly exposed in frame initial 
   Prop will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/PROP.NRLIB/PROP
   LinearOperator is now explicitly exposed in frame initial 
   LinearOperator will be automatically loaded when needed from 
      /var/aw/var/LatexWiki/LOP.NRLIB/LOP
L:=LOP(OVAR ['1,'2], EXPR INT)

$\label{eq1}\hbox{\axiomType{LinearOperator}\ } \left({{\hbox{\axiomType{OrderedVariableList}\ } \left({\left[ 1, \: 2 \right]}\right)}, \:{\hbox{\axiomType{Expression}\ } \left({\hbox{\axiomType{Integer}\ }}\right)}}\right)$

(1)

Type: Type

fricas

-- basis
dx:=basisIn()$L

$\label{eq2}\left[{|_{\ }^{1}}, \:{|_{\ }^{2}}\right]$

(2)

Type: List(LinearOperator(OrderedVariableList([1,2]),Expression(Integer)))

fricas

Dx:=basisOut()$L

$\label{eq3}\left[{|_{1}}, \:{|_{2}}\right]$

(3)

Type: List(LinearOperator(OrderedVariableList([1,2]),Expression(Integer)))

fricas

-- summation
macro Σ(f,b,i) == reduce(+,[f*b.i for i in 1..#b])

Type: Void

fricas

-- identity
I:L:=[1]

$\label{eq4}{|_{1}^{1}}+{|_{2}^{2}}$

(4)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

-- twist
X:L:=[2,1]

$\label{eq5}{|_{1 \ 1}^{1 \ 1}}+{|_{2 \ 1}^{1 \ 2}}+{|_{1 \ 2}^{2 \ 1}}+{|_{2 \ 2}^{2 \ 2}}$

(5)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

-- co-evaluation
Λ:L:=co(1)

$\label{eq6}{|_{1 \ 1}}+{|_{2 \ 2}}$

(6)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

-- evaluation
V:L:=ev(1)

$\label{eq7}{|_{\ }^{1 \ 1}}+{|_{\ }^{2 \ 2}}$

(7)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

Algebra

An n-dimensional algebra is represented by a (2,1)-tensor $Y=\{ {y^k}_{ij} \ i,j,k =1,2, ... n \}$ viewed as a linear operator with two inputs and one output . For example in 2 dimensions

fricas

Y:=Σ(Σ(Σ(script(y,[[i,j],[k]]),dx,i),dx,j),Dx,k)

$\label{eq8}\begin{array}{@{}l} \displaystyle {{y_{1, \: 1}^{1}}\ {|_{1}^{1 \ 1}}}+{{y_{1, \: 1}^{2}}\ {|_{2}^{1 \ 1}}}+{{y_{1, \: 2}^{1}}\ {|_{1}^{1 \ 2}}}+{{y_{1, \: 2}^{2}}\ {|_{2}^{1 \ 2}}}+ \ \ \displaystyle {{y_{2, \: 1}^{1}}\ {|_{1}^{2 \ 1}}}+{{y_{2, \: 1}^{2}}\ {|_{2}^{2 \ 1}}}+{{y_{2, \: 2}^{1}}\ {|_{1}^{2 \ 2}}}+{{y_{2, \: 2}^{2}}\ {|_{2}^{2 \ 2}}}$

(8)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

Multiplication

Given two vectors $P=\{ p^i \}$ and $Q=\{ q^j \}$

fricas

P:=Σ(script(p,[[],[i]]),Dx,i)

$\label{eq9}{{p^{1}}\ {|_{1}}}+{{p^{2}}\ {|_{2}}}$

(9)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

Q:=Σ(script(q,[[],[i]]),Dx,i)

$\label{eq10}{{q^{1}}\ {|_{1}}}+{{q^{2}}\ {|_{2}}}$

(10)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

the tensor operates on their tensor product to yield a vector $R=\{ r_k = {y^k}_{ij} p^i q^j \}$

fricas

R:=(P,Q)/Y

$\label{eq11}\begin{array}{@{}l} \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{p^{2}}\ {q^{2}}\ {y_{2, \: 2}^{1}}}+{{p^{2}}\ {q^{1}}\ {y_{2, \: 1}^{1}}}+{{p^{1}}\ {q^{2}}\ {y_{1, \: 2}^{1}}}+ \ \ \displaystyle {{p^{1}}\ {q^{1}}\ {y_{1, \: 1}^{1}}}$

(11)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

Pictorially:

  P Q
   Y
   R

  or more explicitly

  Pi Qj
   \/
    \
     Rk

Associator

An algebra is said to be associative if:

    Y    =    Y
     Y       Y

    i   j   k   i  j     k   i     j  k
     \  |  /     \/     /     \     \/
      \ | /       \    /       \    /
       \|/    =    e  k    -    i  e
        |           \/           \/
        |            \           /
        l             l         l

This requires that the following (3,1)-tensor

$\label{eq12} \Psi = \{ {\psi_l}^{ijk} = {y^e}_{ij} {y^l}_{ek} - {y^l}_{ie} {y^e}_{jk} \}$

(12)

(associator) is zero.

fricas

YY := (Y,I)/Y - (I,Y)/Y

$\label{eq13}\begin{array}{@{}l} \displaystyle {{\left({{y_{1, \: 1}^{2}}\ {y_{2, \: 1}^{1}}}-{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}\right)}\ {|_{1}^{1 \ 1 \ 1}}}+ \ \ \displaystyle {{\left({{y_{1, \: 1}^{2}}\ {y_{2, \: 1}^{2}}}-{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{2}}}\right)}\ {|_{2}^{1 \ 1 \ 1}}}+ \ \ \displaystyle {{\left({{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{1}}}-{{y_{1, \: 2}^{1}}\ {y_{1, \: 2}^{2}}}\right)}\ {|_{1}^{1 \ 1 \ 2}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{2}}}-{{y_{1, \: 2}^{2}}^{2}}+{{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{2}}}- \ \ \displaystyle {{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}$

(13)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

Commutator

The algebra is commutative if:

    Y = Y

    i   j     i  j     j  i
     \ /   =   \/   -   \/
      |         \       /
      k          k     k

This requires that the following (2,1)-tensor

$\label{eq14} \mathcal{C} = \{ {c^k}_{ij} = {y^k}_{ij} - {y^k}_{ji} \}$

(14)

(commutator) is zero.

fricas

YC:=Y-(X/Y)

$\label{eq15}\begin{array}{@{}l} \displaystyle {{\left(-{y_{2, \: 1}^{1}}+{y_{1, \: 2}^{1}}\right)}\ {|_{1}^{1 \ 2}}}+{{\left(-{y_{2, \: 1}^{2}}+{y_{1, \: 2}^{2}}\right)}\ {|_{2}^{1 \ 2}}}+ \ \ \displaystyle {{\left({y_{2, \: 1}^{1}}-{y_{1, \: 2}^{1}}\right)}\ {|_{1}^{2 \ 1}}}+{{\left({y_{2, \: 1}^{2}}-{y_{1, \: 2}^{2}}\right)}\ {|_{2}^{2 \ 1}}}$

(15)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

A basis for the ideal defined by the coefficients of the commutator is given by:

fricas

groebner(map(x+->x,ravel(YC))$LIST2(EXPR INT,POLY INT))

$\label{eq16}\left[{{y_{2, \: 1}^{2}}-{y_{1, \: 2}^{2}}}, \:{{y_{2, \: 1}^{1}}-{y_{1, \: 2}^{1}}}\right]$

(16)

Type: List(Polynomial(Integer))

Anti-commutator

The algebra is anti-commutative if:

    Y = -Y

    i   j     i  j     j  i
     \ /   =   \/   =   \/
      |         \       /
      k          k     k

This requires that the following (2,1)-tensor

$\label{eq17} \mathcal{A} = \{ {a^k}_{ij} = {y^k}_{ij} + {y^k}_{ji} \}$

(17)

(anti-commutator) is zero.

fricas

YA:=Y+(X/Y)

$\label{eq18}\begin{array}{@{}l} \displaystyle {2 \ {y_{1, \: 1}^{1}}\ {|_{1}^{1 \ 1}}}+{2 \ {y_{1, \: 1}^{2}}\ {|_{2}^{1 \ 1}}}+{{\left({y_{2, \: 1}^{1}}+{y_{1, \: 2}^{1}}\right)}\ {|_{1}^{1 \ 2}}}+ \ \ \displaystyle {{\left({y_{2, \: 1}^{2}}+{y_{1, \: 2}^{2}}\right)}\ {|_{2}^{1 \ 2}}}+{{\left({y_{2, \: 1}^{1}}+{y_{1, \: 2}^{1}}\right)}\ {|_{1}^{2 \ 1}}}+ \ \ \displaystyle {{\left({y_{2, \: 1}^{2}}+{y_{1, \: 2}^{2}}\right)}\ {|_{2}^{2 \ 1}}}+{2 \ {y_{2, \: 2}^{1}}\ {|_{1}^{2 \ 2}}}+{2 \ {y_{2, \: 2}^{2}}\ {|_{2}^{2 \ 2}}}$

(18)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

A basis for the ideal defined by the coefficients of the commutator is given by:

fricas

groebner(map(x+->x,ravel(YA))$LIST2(EXPR INT,POLY INT))

$\label{eq19}\left[{y_{2, \: 2}^{2}}, \:{y_{2, \: 2}^{1}}, \:{{y_{2, \: 1}^{2}}+{y_{1, \: 2}^{2}}}, \:{{y_{2, \: 1}^{1}}+{y_{1, \: 2}^{1}}}, \:{y_{1, \: 1}^{2}}, \:{y_{1, \: 1}^{1}}\right]$

(19)

Type: List(Polynomial(Integer))

Jacobi

The Jacobi identity is:

              X
    Y =  Y + Y
     Y  Y     Y

    i     j     k  i      j     k  i     j      k   i  j   k
     \    |    /    \    /     /    \     \    /     \  \ /
      \   |   /      \  /     /      \     \  /       \  0
       \  |  /        \/     /        \     \/         \/ \
        \ | /          \    /          \    /           \  \
         \|/     =      e  k      -     i  e       -     e  j
          |              \/              \/               \/
          |               \              /                /
          l                l            l                 l

An algebra satisfies the Jacobi identity if and only if the following (3,1)-tensor

$\label{eq20} \Theta = \{ {\theta^l}_{ijk} = {y^l}_{ek} {y^e}_{ij} - {y^l}_{ie} {y^e}_{jk} - {y^l}_{ej} {y^e}_{ik} \}$

(20)

is zero.

fricas

YX := YY - (I,X)/(Y,I)/Y

$\label{eq21}\begin{array}{@{}l} \displaystyle {{\left(-{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}-{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{1}^{1 \ 1 \ 1}}}+ \ \ \displaystyle {{\left(-{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{2}}}-{{y_{1, \: 1}^{1}}\ {y_{1, \: 1}^{2}}}\right)}\ {|_{2}^{1 \ 1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{1}}}-{{y_{1, \: 2}^{2}}\ {y_{2, \: 1}^{1}}}-{{y_{1, \: 2}^{1}}\ {y_{1, \: 2}^{2}}}- \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{1}}}$

(21)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

Scalar Product

A scalar product is denoted by the (2,0)-tensor $U = \{ u_{ij} \}$

fricas

U:=Σ(Σ(script(u,[[],[i,j]]),dx,i),dx,j)

$\label{eq22}{{u^{1, \: 1}}\ {|_{\ }^{1 \ 1}}}+{{u^{1, \: 2}}\ {|_{\ }^{1 \ 2}}}+{{u^{2, \: 1}}\ {|_{\ }^{2 \ 1}}}+{{u^{2, \: 2}}\ {|_{\ }^{2 \ 2}}}$

(22)

Type: LinearOperator(OrderedVariableList([1,2]),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:

    i  j  k   i  j  k   i  j  k
     \ | /     \/  /     \  \/
      \|/   =   \ /   -   \ /
       0         0         0

$\label{eq23} \Phi = \{ \phi^{ijk} = {y^e}_{ij} u_{ek} - u_{ie} {y_e}^{jk} \}$

(23)

(three-point function) is zero.

fricas

YU := (Y,I)/U - (I,Y)/U

$\label{eq24}\begin{array}{@{}l} \displaystyle {{\left({u^{2, \: 1}}-{u^{1, \: 2}}\right)}\ {y_{1, \: 1}^{2}}\ {|_{\ }^{1 \ 1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle -{{u^{1, \: 2}}\ {y_{1, \: 2}^{2}}}-{{u^{1, \: 1}}\ {y_{1, \: 2}^{1}}}+{{u^{2, \: 2}}\ {y_{1, \: 1}^{2}}}+ \ \ \displaystyle {{u^{1, \: 2}}\ {y_{1, \: 1}^{1}}}$

(24)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

Definition 2

An algebra with a non-degenerate associative scalar product is called pre-Frobenius.

We may consider the problem where multiplication Y is given, and look for all associative scalar products or we may consider an scalar product U as given, and look for all algebras such that the scalar product is associative.

This problem can be solved using linear algebra.

fricas

)expose MCALCFN

   MultiVariableCalculusFunctions is now explicitly exposed in frame 
      initial 
K := jacobian(ravel(YU),concat(map(variables,ravel(Y)))::List Symbol);

Type: Matrix(Expression(Integer))

fricas

yy := transpose matrix [concat(map(variables,ravel(Y)))::List Symbol];

Type: Matrix(Polynomial(Integer))

fricas

K::OutputForm * yy::OutputForm = 0

$\label{eq25}\begin{array}{@{}l} \displaystyle {{\left[ \begin{array}{cccccccc} 0 &{{u^{2, \: 1}}-{u^{1, \: 2}}}& 0 & 0 & 0 & 0 & 0 & 0 \ {u^{1, \: 2}}&{u^{2, \: 2}}& -{u^{1, \: 1}}& -{u^{1, \: 2}}& 0 & 0 & 0 & 0 \ 0 & 0 &{u^{1, \: 1}}&{u^{2, \: 1}}& -{u^{1, \: 1}}& -{u^{1, \: 2}}& 0 & 0 \ 0 & 0 &{u^{1, \: 2}}&{u^{2, \: 2}}& 0 & 0 & -{u^{1, \: 1}}& -{u^{1, \: 2}} \ -{u^{2, \: 1}}& -{u^{2, \: 2}}& 0 & 0 &{u^{1, \: 1}}&{u^{2, \: 1}}& 0 & 0 \ 0 & 0 & -{u^{2, \: 1}}& -{u^{2, \: 2}}&{u^{1, \: 2}}&{u^{2, \: 2}}& 0 & 0 \ 0 & 0 & 0 & 0 & -{u^{2, \: 1}}& -{u^{2, \: 2}}&{u^{1, \: 1}}&{u^{2, \: 1}} \ 0 & 0 & 0 & 0 & 0 & 0 &{-{u^{2, \: 1}}+{u^{1, \: 2}}}& 0$

(25)

Type: Equation(OutputForm?)

The matrix K transforms the coefficients of the tensor into coefficients of the tensor $\Phi$ . We are looking for coefficients of the tensor such that K transforms the tensor into $\Phi=0$ for any .

A necessary condition for the equation to have a non-trivial solution is that the matrix K be degenerate.

Theorem 1

All 2-dimensional pre-Frobenius algebras are symmetric.

Proof: Consider the determinant of the matrix K above.

fricas

Kd := factor(determinant(K)::DMP(concat map(variables,ravel(U)),FRAC INT))

$\label{eq26}{{\left({u^{1, \: 2}}-{u^{2, \: 1}}\right)}^{4}}\ {{\left({{u^{1, \: 1}}\ {u^{2, \: 2}}}-{{u^{1, \: 2}}\ {u^{2, \: 1}}}\right)}^{2}}$

(26)

Type: Factored(DistributedMultivariatePolynomial?([u[;1,1],u[;1,2],u[;2,1],u[;2,2]],Fraction(Integer)))

The scalar product must also be non-degenerate

fricas

Ud:DMP(concat map(variables,ravel(U)),FRAC INT) := determinant [[retract((Dx.i,Dx.j)/U) for j in 1..#Dx] for i in 1..#Dx]

$\label{eq27}{{u^{1, \: 1}}\ {u^{2, \: 2}}}-{{u^{1, \: 2}}\ {u^{2, \: 1}}}$

(27)

Type: DistributedMultivariatePolynomial?([u[;1,1],u[;1,2],u[;2,1],u[;2,2]],Fraction(Integer))

therefore U must be symmetric.

fricas

nthFactor(Kd,1)

   There are no exposed library operations named nthFactor but there 
      are 3 unexposed operations with that name. Use HyperDoc Browse or
      issue
                            )display op nthFactor
      to learn more about the available operations.

   Cannot find a definition or applicable library operation named 
      nthFactor with argument type(s) 
Factored(DistributedMultivariatePolynomial([u[;1,1],u[;1,2],u[;2,1],u[;2,2]],Fraction(Integer)))
                               PositiveInteger

      Perhaps you should use "@" to indicate the required return type, 
      or "$" to specify which version of the function you need.

Theorem 2

All 2-dimensional algebras with associative scalar product are commutative.

Proof: The basis of the null space of the symmetric K matrix are all symmetric

fricas

YUS := (I,Y)/US - (Y,I)/US

   There are 15 exposed and 15 unexposed library operations named / 
      having 2 argument(s) but none was determined to be applicable. 
      Use HyperDoc Browse, or issue
                                )display op /
      to learn more about the available operations. Perhaps 
      package-calling the operation or using coercions on the arguments
      will allow you to apply the operation.

   Cannot find a definition or applicable library operation named / 
      with argument type(s) 
    Tuple(LinearOperator(OrderedVariableList([1,2]),Expression(Integer)))
                                Variable(US)

      Perhaps you should use "@" to indicate the required return type, 
      or "$" to specify which version of the function you need.

This defines a 4-parameter family of 2-d pre-Frobenius algebras

fricas

test(eval(YUS,SS)=0*YUS)

   There are 10 exposed and 6 unexposed library operations named eval 
      having 2 argument(s) but none was determined to be applicable. 
      Use HyperDoc Browse, or issue
                              )display op eval
      to learn more about the available operations. Perhaps 
      package-calling the operation or using coercions on the arguments
      will allow you to apply the operation.

   Cannot find a definition or applicable library operation named eval 
      with argument type(s) 
                                Variable(YUS)
                                Variable(SS)

      Perhaps you should use "@" to indicate the required return type, 
      or "$" to specify which version of the function you need.

Alternatively we may consider

fricas

J := jacobian(ravel(YU),concat(map(variables,ravel(U)))::List Symbol);

Type: Matrix(Expression(Integer))

fricas

uu := transpose matrix [concat(map(variables,ravel(U)))::List Symbol];

Type: Matrix(Polynomial(Integer))

fricas

J::OutputForm * uu::OutputForm = 0

$\label{eq28}\begin{array}{@{}l} \displaystyle {{\left[ \begin{array}{cccc} 0 & -{y_{1, \: 1}^{2}}&{y_{1, \: 1}^{2}}& 0 \ -{y_{1, \: 2}^{1}}&{-{y_{1, \: 2}^{2}}+{y_{1, \: 1}^{1}}}& 0 &{y_{1, \: 1}^{2}} \ {-{y_{2, \: 1}^{1}}+{y_{1, \: 2}^{1}}}& -{y_{2, \: 1}^{2}}&{y_{1, \: 2}^{2}}& 0 \ -{y_{2, \: 2}^{1}}&{-{y_{2, \: 2}^{2}}+{y_{1, \: 2}^{1}}}& 0 &{y_{1, \: 2}^{2}} \ {y_{2, \: 1}^{1}}& 0 &{{y_{2, \: 1}^{2}}-{y_{1, \: 1}^{1}}}& -{y_{1, \: 1}^{2}} \ 0 &{y_{2, \: 1}^{1}}& -{y_{1, \: 2}^{1}}&{{y_{2, \: 1}^{2}}-{y_{1, \: 2}^{2}}} \ {y_{2, \: 2}^{1}}& 0 &{{y_{2, \: 2}^{2}}-{y_{2, \: 1}^{1}}}& -{y_{2, \: 1}^{2}} \ 0 &{y_{2, \: 2}^{1}}& -{y_{2, \: 2}^{1}}& 0$

(28)

Type: Equation(OutputForm?)

The matrix J transforms the coefficients of the tensor into coefficients of the tensor $\Phi$ . We are looking for coefficients of the tensor such that J transforms the tensor into $\Phi=0$ for any .

A necessary condition for the equation to have a non-trivial solution is that all 70 of the 4x4 sub-matrices of J are degenerate. To this end we can form the polynomial ideal of the determinants of these sub-matrices.

fricas

JP:=ideal concat concat concat
  [[[[ determinant(
    matrix([row(J,i1),row(J,i2),row(J,i3),row(J,i4)]))::FRAC POLY INT
      for i4 in (i3+1)..maxRowIndex(J) ] 
        for i3 in (i2+1)..(maxRowIndex(J)-1) ]
          for i2 in (i1+1)..(maxRowIndex(J)-2) ]
            for i1 in minRowIndex(J)..(maxRowIndex(J)-3) ];

Type: PolynomialIdeal?(Fraction(Integer),IndexedExponents?(Symbol),Symbol,Polynomial(Fraction(Integer)))

fricas

#generators(%)

$\label{eq29}51$

(29)

Type: PositiveInteger?

Theorem 3

If a 2-d algebra is associative, commutative, anti-commutative or if it satisfies the Jacobi identity then it is a pre-Frobenius algebra.

Proof

Consider the ideals of the associator, commutator, anti-commutator and Jacobi identity

fricas

YYI:=ideal(ravel(YY)::List FRAC POLY INT);

Type: PolynomialIdeal?(Fraction(Integer),IndexedExponents?(Symbol),Symbol,Polynomial(Fraction(Integer)))

fricas

in?(JP,YYI)  -- associative

$\label{eq30} \mbox{\rm true}$

(30)

Type: Boolean

fricas

YCI:=ideal(ravel(YC)::List FRAC POLY INT);

Type: PolynomialIdeal?(Fraction(Integer),IndexedExponents?(Symbol),Symbol,Polynomial(Fraction(Integer)))

fricas

in?(JP,YCI)  -- commutative

$\label{eq31} \mbox{\rm true}$

(31)

Type: Boolean

fricas

YAI:=ideal(ravel(YA)::List FRAC POLY INT);

Type: PolynomialIdeal?(Fraction(Integer),IndexedExponents?(Symbol),Symbol,Polynomial(Fraction(Integer)))

fricas

in?(JP,YAI)  -- anti-commutative

$\label{eq32} \mbox{\rm true}$

(32)

Type: Boolean

fricas

YXI:=ideal(ravel(YX)::List FRAC POLY INT);

Type: PolynomialIdeal?(Fraction(Integer),IndexedExponents?(Symbol),Symbol,Polynomial(Fraction(Integer)))

fricas

in?(JP,YXI) -- Jacobi identity

$\label{eq33} \mbox{\rm true}$

(33)

Type: Boolean

Y-forms

Three traces of two graftings of an algebra gives six (2,0)-forms.

Left snail and right snail:

  LS                    RS

  Y /\                    /\ Y
   Y  )                  (  Y
    \/                    \/

  i  j                        j  i
   \/                          \/
    \    /\              /\    /
     e  f  \            /  f  e
      \/    \          /    \/
       \    /          \    /
        f  /            \  f
         \/              \/

$\label{eq34} LS = \{ {y^e}_{ij} {y^f}_{ef} \} \ RS = \{ {y^f}_{fe} {y^e}_{ji} \}$

(34)

fricas

LS:=
  ( Y Λ  )/ _
  (  Y I )/ _
      V

$\label{eq35}\begin{array}{@{}l} \displaystyle {{\left({{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 1}^{1}}}+{{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{2}}}+{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{\ }^{1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 2}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 2}^{2}}\ {y_{2, \: 1}^{1}}}+{{y_{1, \: 2}^{1}}\ {y_{1, \: 2}^{2}}}+ \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{1}}}$

(35)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

RS:=
  (  Λ Y )/ _
  ( I Y  )/ _
     V

$\label{eq36}\begin{array}{@{}l} \displaystyle {{\left({{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 1}^{1}}\ {y_{2, \: 1}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}+{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{\ }^{1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 2}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 2}^{1}}\ {y_{2, \: 1}^{2}}}+{{y_{1, \: 2}^{1}}\ {y_{1, \: 2}^{2}}}+ \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{1}}}$

(36)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

test(LS=RS)

$\label{eq37} \mbox{\rm false}$

(37)

Type: Boolean

Left and right deer:

   RD                 LD

   \ /\/              \/\ /
    Y /\              /\ Y
     Y  )            (  Y
      \/              \/

   i            j    i            j
    \    /\    /      \    /\    /
     \  f  \  /        \  /  f  /
      \/    \/          \/    \/
       \    /\          /\    /
        e  /  \        /  \  e
         \/    \      /    \/
          \    /      \    /
           f  /        \  f
            \/          \/

$\label{eq38} RD = \{ {y^e}_{if} {y^f}_{ej} \} \ LD = \{ {y^f}_{ie} {y^e}_{fj} \}$

(38)

Left and right deer forms are identical but different from snails.

fricas

RD:=
  (  I Λ I  ) / _
  (   Y X   ) / _
  (    Y I  ) / _
        V

$\label{eq39}\begin{array}{@{}l} \displaystyle {{\left({{y_{1, \: 2}^{2}}\ {y_{2, \: 1}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 1}^{1}}}+{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}+{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{\ }^{1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 2}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{1}}}+{{y_{1, \: 2}^{1}}\ {y_{1, \: 2}^{2}}}+ \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{1}}}$

(39)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

LD:=
  (  I Λ I  ) / _
  (   X Y   ) / _
  (  I Y    ) / _
      V

$\label{eq40}\begin{array}{@{}l} \displaystyle {{\left({{y_{1, \: 2}^{2}}\ {y_{2, \: 1}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 1}^{1}}}+{{y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}+{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{\ }^{1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 2}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{1}}}+{{y_{1, \: 2}^{1}}\ {y_{1, \: 2}^{2}}}+ \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{1}}}$

(40)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

test(LD=RD)

$\label{eq41} \mbox{\rm true}$

(41)

Type: Boolean

fricas

test(RD=RS)

$\label{eq42} \mbox{\rm false}$

(42)

Type: Boolean

fricas

test(RD=LS)

$\label{eq43} \mbox{\rm false}$

(43)

Type: Boolean

Left and right turtles:

  RT                   LT

   /\ / /               \ \ /\
  (  Y /                 \ Y  )
   \  Y                   Y  /
    \/                     \/

           i     j      i     j
    /\    /     /        \     \    /\
   /  f  /     /          \     \  f  \
  /    \/     /            \     \/    \
  \     \    /              \    /     /
   \     e  /                \  e     /
    \     \/                  \/     /
     \    /                    \    /
      \  f                      f  /
       \/                        \/

$\label{eq44} RT = \{ {y^e}_{fi} {y^f}_{ej} \} \ LT = \{ {y^f}_{ie} {y^e}_{jf} \}$

(44)

fricas

RT:=
  (  Λ I I ) / _
  ( I Y I  ) / _
  (  I Y   ) / _
      V

$\label{eq45}\begin{array}{@{}l} \displaystyle {{\left({{y_{2, \: 1}^{2}}^{2}}+{2 \ {y_{1, \: 1}^{2}}\ {y_{2, \: 1}^{1}}}+{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{\ }^{1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{2, \: 1}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{1}}}+{{y_{1, \: 2}^{2}}\ {y_{2, \: 1}^{1}}}+ \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{1, \: 2}^{1}}}$

(45)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

LT:=
  ( I I Λ  ) / _
  (  I Y I ) / _
  (   Y I  ) / _
       V

$\label{eq46}\begin{array}{@{}l} \displaystyle {{\left({{y_{1, \: 2}^{2}}^{2}}+{2 \ {y_{1, \: 1}^{2}}\ {y_{1, \: 2}^{1}}}+{{y_{1, \: 1}^{1}}^{2}}\right)}\ {|_{\ }^{1 \ 1}}}+ \ \ \displaystyle {{\left({ \begin{array}{@{}l} \displaystyle {{y_{1, \: 2}^{2}}\ {y_{2, \: 2}^{2}}}+{{y_{1, \: 1}^{2}}\ {y_{2, \: 2}^{1}}}+{{y_{1, \: 2}^{1}}\ {y_{2, \: 1}^{2}}}+ \ \ \displaystyle {{y_{1, \: 1}^{1}}\ {y_{2, \: 1}^{1}}}$

(46)

Type: LinearOperator(OrderedVariableList([1,2]),Expression(Integer))

fricas

test(LT=RT)

$\label{eq47} \mbox{\rm false}$

(47)

Type: Boolean

The turles are symmetric

fricas

test(RT = X/RT)

$\label{eq48} \mbox{\rm true}$

(48)

Type: Boolean

fricas

test(LT = X/LT)

$\label{eq49} \mbox{\rm true}$

(49)

Type: Boolean

Five of the six forms are independent.

fricas

test(RT=RS)

$\label{eq50} \mbox{\rm false}$

(50)

Type: Boolean

fricas

test(RT=LS)

$\label{eq51} \mbox{\rm false}$

(51)

Type: Boolean

fricas

test(RT=RD)

$\label{eq52} \mbox{\rm false}$

(52)

Type: Boolean

fricas

test(LT=RS)

$\label{eq53} \mbox{\rm false}$

(53)

Type: Boolean

fricas

test(LT=LS)

$\label{eq54} \mbox{\rm false}$

(54)

Type: Boolean

fricas

test(LT=RD)

$\label{eq55} \mbox{\rm false}$

(55)

Type: Boolean

Associativity implies right turtle equals right snail and left turtle equals left snail.

fricas

in?(ideal(ravel(RT-RS)::List FRAC POLY INT),YYI)

$\label{eq56} \mbox{\rm true}$

(56)

Type: Boolean

fricas

in?(ideal(ravel(LT-LS)::List FRAC POLY INT),YYI)

$\label{eq57} \mbox{\rm true}$

(57)

Type: Boolean

If the Jacobi identity holds then both snails are zero

fricas

in?(ideal(ravel(RS)::List FRAC POLY INT),YXI)

$\label{eq58} \mbox{\rm true}$

(58)

Type: Boolean

fricas

in?(ideal(ravel(LS)::List FRAC POLY INT),YXI)

$\label{eq59} \mbox{\rm true}$

(59)

Type: Boolean

and right turtle and deer have opposite signs

fricas

in?(ideal(ravel(RT+RD)::List FRAC POLY INT),YXI)

$\label{eq60} \mbox{\rm false}$

(60)

Type: Boolean