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PencilsOfQuadrics :: cliffordOperators

cliffordOperators -- Generators for a Clifford Algebra

Synopsis

Description

The Clifford algebra C := Cliff(qq) of a quadratic form qq in n=2d variables is a free ZZ/2-graded algebra of rank 2^{n} where n = numgens S-numgens R (if R is ZZ-graded, and M1, M2 are linear in the variables of R, then C inherits a ZZ-grading; this is our usual case. As an R-module C = C0++C1, with each component of rank 2^{(n-1)}. The operators eOdd_i go from C1 to C0; the operators eEv go from C0 to C1.

We have eOdd_i*eEv_j+eOdd_j*eEv_i = B(e_i,e_j), where the e_i form a basis of the space on which qq acts and B is the bilinear form associated to 2qq thus the the pairs (eOd_i,eEv_i) form a representation of Cliff(qq).

In the following we construct the generic symmetric bilinear form on 2d variables and make a quadratic form qq out of it.

i1 : kk=ZZ/101; d=1;
i3 : n=2*d

o3 = 2
i4 : R=kk[a_0..a_(binomial(n+2,2))]

o4 = R

o4 : PolynomialRing
i5 : S=kk[x_0..x_(n-1),a_0..a_(binomial(n+2,2))]

o5 = S

o5 : PolynomialRing
i6 : M=genericSymmetricMatrix(S,a_0,n)

o6 = | a_0 a_1 |
     | a_1 a_2 |

             2       2
o6 : Matrix S  <--- S
i7 : X=(vars S)_{0..n-1}

o7 = | x_0 x_1 |

             1       2
o7 : Matrix S  <--- S
i8 : Y=X*M

o8 = | x_0a_0+x_1a_1 x_0a_1+x_1a_2 |

             1       2
o8 : Matrix S  <--- S
i9 : qq = X*transpose Y

o9 = | x_0^2a_0+2x_0x_1a_1+x_1^2a_2 |

             1       1
o9 : Matrix S  <--- S
i10 : (M1,M2)=matrixFactorizationK(X,Y);
i11 : (eOdd,eEv)=cliffordOperators(M1,M2,R);

we check two of the relations of the Clifford algebra:

i12 : (eOdd_0*eEv_0+eOdd_0*eEv_0)_(0,0) == 2*R_0

o12 = true
i13 : (eOdd_0*eEv_1+eOdd_1*eEv_0)_(0,0) == 2*R_1

o13 = true

See also

Ways to use cliffordOperators :

For the programmer

The object cliffordOperators is a method function.