X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Feja%2Feja_algebra.py;h=d90d3f2dcb5f4adc5cd6135ac4151ef63c3166c8;hb=6c983c4d14a02b4eff37fd2a07ae6b32b93e611c;hp=d0e7b074ce41a00f66d6f6dcd487653f3a8b1674;hpb=11e681d6320f0b7ddbb834931845b6f4a745da93;p=sage.d.git diff --git a/mjo/eja/eja_algebra.py b/mjo/eja/eja_algebra.py index d0e7b07..d90d3f2 100644 --- a/mjo/eja/eja_algebra.py +++ b/mjo/eja/eja_algebra.py @@ -60,6 +60,9 @@ class FiniteDimensionalEuclideanJordanAlgebra(CombinatorialFreeModule): self._rank = rank self._natural_basis = natural_basis + # TODO: HACK for the charpoly.. needs redesign badly. + self._basis_normalizers = None + if category is None: category = MagmaticAlgebras(field).FiniteDimensional() category = category.WithBasis().Unital() @@ -224,6 +227,7 @@ class FiniteDimensionalEuclideanJordanAlgebra(CombinatorialFreeModule): return V.span_of_basis(b) + @cached_method def _charpoly_coeff(self, i): """ @@ -234,6 +238,19 @@ class FiniteDimensionalEuclideanJordanAlgebra(CombinatorialFreeModule): store the trace/determinant (a_{r-1} and a_{0} respectively) separate from the entire characteristic polynomial. """ + if self._basis_normalizers is not None: + # Must be a matrix class? + # WARNING/TODO: this whole mess is mis-designed. + n = self.natural_basis_space().nrows() + field = self.base_ring().base_ring() # yeeeeaaaahhh + J = self.__class__(n, field, False) + (_,x,_,_) = J._charpoly_matrix_system() + p = J._charpoly_coeff(i) + # p might be missing some vars, have to substitute "optionally" + pairs = zip(x.base_ring().gens(), self._basis_normalizers) + substitutions = { v: v*c for (v,c) in pairs } + return p.subs(substitutions) + (A_of_x, x, xr, detA) = self._charpoly_matrix_system() R = A_of_x.base_ring() if i >= self.rank(): @@ -418,7 +435,7 @@ class FiniteDimensionalEuclideanJordanAlgebra(CombinatorialFreeModule): """ X = x.natural_representation() Y = y.natural_representation() - return self.__class__.natural_inner_product(X,Y) + return self.natural_inner_product(X,Y) def is_trivial(self): @@ -781,7 +798,7 @@ class RealCartesianProductEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: y = J.random_element() sage: X = x.natural_representation() sage: Y = y.natural_representation() - sage: x.inner_product(y) == J.__class__.natural_inner_product(X,Y) + sage: x.inner_product(y) == J.natural_inner_product(X,Y) True """ @@ -924,7 +941,7 @@ def _complex_hermitian_basis(n, field): -def _quaternion_hermitian_basis(n, field, normalize): +def _quaternion_hermitian_basis(n, field): """ Returns a basis for the space of quaternion Hermitian n-by-n matrices. @@ -942,7 +959,7 @@ def _quaternion_hermitian_basis(n, field, normalize): sage: set_random_seed() sage: n = ZZ.random_element(1,5) - sage: B = _quaternion_hermitian_basis(n, QQ, False) + sage: B = _quaternion_hermitian_basis(n, QQ) sage: all( M.is_symmetric() for M in B ) True @@ -1215,7 +1232,10 @@ def _unembed_quaternion_matrix(M): if not n.mod(4).is_zero(): raise ValueError("the matrix 'M' must be a complex embedding") - Q = QuaternionAlgebra(QQ,-1,-1) + # Use the base ring of the matrix to ensure that its entries can be + # multiplied by elements of the quaternion algebra. + field = M.base_ring() + Q = QuaternionAlgebra(field,-1,-1) i,j,k = Q.gens() # Go top-left to bottom-right (reading order), converting every @@ -1229,8 +1249,10 @@ def _unembed_quaternion_matrix(M): raise ValueError('bad on-diagonal submatrix') if submat[0,1] != -submat[1,0].conjugate(): raise ValueError('bad off-diagonal submatrix') - z = submat[0,0].real() + submat[0,0].imag()*i - z += submat[0,1].real()*j + submat[0,1].imag()*k + z = submat[0,0].vector()[0] # real part + z += submat[0,0].vector()[1]*i # imag part + z += submat[0,1].vector()[0]*j # real part + z += submat[0,1].vector()[1]*k # imag part elements.append(z) return matrix(Q, n/4, elements) @@ -1308,7 +1330,8 @@ class RealSymmetricEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: (x*y).inner_product(z) == y.inner_product(x*z) True - Our basis is normalized with respect to the natural inner product:: + Our natural basis is normalized with respect to the natural inner + product unless we specify otherwise:: sage: set_random_seed() sage: n = ZZ.random_element(1,5) @@ -1316,8 +1339,11 @@ class RealSymmetricEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: all( b.norm() == 1 for b in J.gens() ) True - Left-multiplication operators are symmetric because they satisfy - the Jordan axiom:: + Since our natural basis is normalized with respect to the natural + inner product, and since we know that this algebra is an EJA, any + left-multiplication operator's matrix will be symmetric because + natural->EJA basis representation is an isometry and within the EJA + the operator is self-adjoint by the Jordan axiom:: sage: set_random_seed() sage: n = ZZ.random_element(1,5) @@ -1338,11 +1364,10 @@ class RealSymmetricEJA(FiniteDimensionalEuclideanJordanAlgebra): p = z**2 - 2 if p.is_irreducible(): field = NumberField(p, 'sqrt2', embedding=RLF(2).sqrt()) - S = [ s.change_ring(field) for s in S ] - self._basis_denormalizers = tuple( - self.__class__.natural_inner_product(s,s).sqrt() - for s in S ) - S = tuple( s/c for (s,c) in zip(S,self._basis_denormalizers) ) + S = [ s.change_ring(field) for s in S ] + self._basis_normalizers = tuple( + ~(self.natural_inner_product(s,s).sqrt()) for s in S ) + S = tuple( s*c for (s,c) in zip(S,self._basis_normalizers) ) Qs = _multiplication_table_from_matrix_basis(S) @@ -1408,7 +1433,8 @@ class ComplexHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: (x*y).inner_product(z) == y.inner_product(x*z) True - Our basis is normalized with respect to the natural inner product:: + Our natural basis is normalized with respect to the natural inner + product unless we specify otherwise:: sage: set_random_seed() sage: n = ZZ.random_element(1,4) @@ -1416,8 +1442,11 @@ class ComplexHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: all( b.norm() == 1 for b in J.gens() ) True - Left-multiplication operators are symmetric because they satisfy - the Jordan axiom:: + Since our natural basis is normalized with respect to the natural + inner product, and since we know that this algebra is an EJA, any + left-multiplication operator's matrix will be symmetric because + natural->EJA basis representation is an isometry and within the EJA + the operator is self-adjoint by the Jordan axiom:: sage: set_random_seed() sage: n = ZZ.random_element(1,5) @@ -1438,11 +1467,10 @@ class ComplexHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): p = z**2 - 2 if p.is_irreducible(): field = NumberField(p, 'sqrt2', embedding=RLF(2).sqrt()) - S = [ s.change_ring(field) for s in S ] - self._basis_denormalizers = tuple( - self.__class__.natural_inner_product(s,s).sqrt() - for s in S ) - S = tuple( s/c for (s,c) in zip(S,self._basis_denormalizers) ) + S = [ s.change_ring(field) for s in S ] + self._basis_normalizers = tuple( + ~(self.natural_inner_product(s,s).sqrt()) for s in S ) + S = tuple( s*c for (s,c) in zip(S,self._basis_normalizers) ) Qs = _multiplication_table_from_matrix_basis(S) @@ -1461,6 +1489,8 @@ class ComplexHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): # The trace need not be real; consider Xu = (i*I) and Yu = I. return ((Xu*Yu).trace()).vector()[0] # real part, I guess + + class QuaternionHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): """ The rank-n simple EJA consisting of self-adjoint n-by-n quaternion @@ -1477,7 +1507,7 @@ class QuaternionHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): The dimension of this algebra is `n^2`:: sage: set_random_seed() - sage: n = ZZ.random_element(1,5) + sage: n = ZZ.random_element(1,4) sage: J = QuaternionHermitianEJA(n) sage: J.dimension() == 2*(n^2) - n True @@ -1485,7 +1515,7 @@ class QuaternionHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): The Jordan multiplication is what we think it is:: sage: set_random_seed() - sage: n = ZZ.random_element(1,5) + sage: n = ZZ.random_element(1,4) sage: J = QuaternionHermitianEJA(n) sage: x = J.random_element() sage: y = J.random_element() @@ -1506,7 +1536,7 @@ class QuaternionHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): Our inner product satisfies the Jordan axiom:: sage: set_random_seed() - sage: n = ZZ.random_element(1,5) + sage: n = ZZ.random_element(1,4) sage: J = QuaternionHermitianEJA(n) sage: x = J.random_element() sage: y = J.random_element() @@ -1514,9 +1544,45 @@ class QuaternionHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: (x*y).inner_product(z) == y.inner_product(x*z) True + Our natural basis is normalized with respect to the natural inner + product unless we specify otherwise:: + + sage: set_random_seed() + sage: n = ZZ.random_element(1,4) + sage: J = QuaternionHermitianEJA(n) + sage: all( b.norm() == 1 for b in J.gens() ) + True + + Since our natural basis is normalized with respect to the natural + inner product, and since we know that this algebra is an EJA, any + left-multiplication operator's matrix will be symmetric because + natural->EJA basis representation is an isometry and within the EJA + the operator is self-adjoint by the Jordan axiom:: + + sage: set_random_seed() + sage: n = ZZ.random_element(1,5) + sage: x = QuaternionHermitianEJA(n).random_element() + sage: x.operator().matrix().is_symmetric() + True + """ def __init__(self, n, field=QQ, normalize_basis=True, **kwargs): - S = _quaternion_hermitian_basis(n, field, normalize_basis) + S = _quaternion_hermitian_basis(n, field) + + if n > 1 and normalize_basis: + # We'll need sqrt(2) to normalize the basis, and this + # winds up in the multiplication table, so the whole + # algebra needs to be over the field extension. + R = PolynomialRing(field, 'z') + z = R.gen() + p = z**2 - 2 + if p.is_irreducible(): + field = NumberField(p, 'sqrt2', embedding=RLF(2).sqrt()) + S = [ s.change_ring(field) for s in S ] + self._basis_normalizers = tuple( + ~(self.natural_inner_product(s,s).sqrt()) for s in S ) + S = tuple( s*c for (s,c) in zip(S,self._basis_normalizers) ) + Qs = _multiplication_table_from_matrix_basis(S) fdeja = super(QuaternionHermitianEJA, self) @@ -1526,17 +1592,16 @@ class QuaternionHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra): natural_basis=S, **kwargs) - def inner_product(self, x, y): - # Since a+bi+cj+dk on the diagonal is represented as - # - # a + bi +cj + dk = [ a b c d] - # [ -b a -d c] - # [ -c d a -b] - # [ -d -c b a], - # - # we'll quadruple-count the "a" entries if we take the trace of - # the embedding. - return _matrix_ip(x,y)/4 + @staticmethod + def natural_inner_product(X,Y): + Xu = _unembed_quaternion_matrix(X) + Yu = _unembed_quaternion_matrix(Y) + # The trace need not be real; consider Xu = (i*I) and Yu = I. + # The result will be a quaternion algebra element, which doesn't + # have a "vector" method, but does have coefficient_tuple() method + # that returns the coefficients of 1, i, j, and k -- in that order. + return ((Xu*Yu).trace()).coefficient_tuple()[0] + class JordanSpinEJA(FiniteDimensionalEuclideanJordanAlgebra): @@ -1631,7 +1696,7 @@ class JordanSpinEJA(FiniteDimensionalEuclideanJordanAlgebra): sage: y = J.random_element() sage: X = x.natural_representation() sage: Y = y.natural_representation() - sage: x.inner_product(y) == J.__class__.natural_inner_product(X,Y) + sage: x.inner_product(y) == J.natural_inner_product(X,Y) True """