from sage.categories.magmatic_algebras import MagmaticAlgebras
from sage.combinat.free_module import CombinatorialFreeModule
from sage.matrix.constructor import matrix
+from sage.matrix.matrix_space import MatrixSpace
from sage.misc.cachefunc import cached_method
from sage.misc.prandom import choice
from sage.misc.table import table
return self.zero()
natural_basis = self.natural_basis()
- if elt not in natural_basis[0].matrix_space():
+ basis_space = natural_basis[0].matrix_space()
+ if elt not in basis_space:
raise ValueError("not a naturally-represented algebra element")
- # Thanks for nothing! Matrix spaces aren't vector
- # spaces in Sage, so we have to figure out its
- # natural-basis coordinates ourselves.
- V = VectorSpace(elt.base_ring(), elt.nrows()*elt.ncols())
+ # Thanks for nothing! Matrix spaces aren't vector spaces in
+ # Sage, so we have to figure out its natural-basis coordinates
+ # ourselves. We use the basis space's ring instead of the
+ # element's ring because the basis space might be an algebraic
+ # closure whereas the base ring of the 3-by-3 identity matrix
+ # could be QQ instead of QQbar.
+ V = VectorSpace(basis_space.base_ring(), elt.nrows()*elt.ncols())
W = V.span_of_basis( _mat2vec(s) for s in natural_basis )
coords = W.coordinate_vector(_mat2vec(elt))
return self.from_vector(coords)
Finite family {0: e0, 1: e1, 2: e2}
sage: J.natural_basis()
(
- [1 0] [0 1] [0 0]
- [0 0], [1 0], [0 1]
+ [1 0] [ 0 1/2*sqrt2] [0 0]
+ [0 0], [1/2*sqrt2 0], [0 1]
)
::
"""
if self._natural_basis is None:
- return tuple( b.to_vector().column() for b in self.basis() )
+ M = self.natural_basis_space()
+ return tuple( M(b.to_vector()) for b in self.basis() )
else:
return self._natural_basis
+ def natural_basis_space(self):
+ """
+ Return the matrix space in which this algebra's natural basis
+ elements live.
+ """
+ if self._natural_basis is None or len(self._natural_basis) == 0:
+ return MatrixSpace(self.base_ring(), self.dimension(), 1)
+ else:
+ return self._natural_basis[0].matrix_space()
+
+
@cached_method
def one(self):
"""
sage: J = RealSymmetricEJA(2)
sage: J.vector_space()
- Vector space of dimension 3 over Rational Field
+ Vector space of dimension 3 over...
"""
return self.zero().to_vector().parent().ambient_vector_space()
sage: RealCartesianProductEJA(3, prefix='r').gens()
(r0, r1, r2)
+ Our inner product satisfies the Jordan axiom::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: J = RealCartesianProductEJA(n)
+ sage: x = J.random_element()
+ sage: y = J.random_element()
+ sage: z = J.random_element()
+ sage: (x*y).inner_product(z) == y.inner_product(x*z)
+ True
+
"""
def __init__(self, n, field=QQ, **kwargs):
V = VectorSpace(field, n)
-def _real_symmetric_basis(n, field=QQ):
+def _real_symmetric_basis(n, field):
"""
Return a basis for the space of real symmetric n-by-n matrices.
+
+ SETUP::
+
+ sage: from mjo.eja.eja_algebra import _real_symmetric_basis
+
+ TESTS::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: B = _real_symmetric_basis(n, QQbar)
+ sage: all( M.is_symmetric() for M in B)
+ True
+
"""
# The basis of symmetric matrices, as matrices, in their R^(n-by-n)
# coordinates.
if i == j:
Sij = Eij
else:
- # Beware, orthogonal but not normalized!
Sij = Eij + Eij.transpose()
+ # Now normalize it.
+ Sij = Sij / _real_symmetric_matrix_ip(Sij,Sij).sqrt()
S.append(Sij)
return tuple(S)
-def _complex_hermitian_basis(n, field=QQ):
+def _complex_hermitian_basis(n, field):
"""
Returns a basis for the space of complex Hermitian n-by-n matrices.
sage: set_random_seed()
sage: n = ZZ.random_element(1,5)
- sage: all( M.is_symmetric() for M in _complex_hermitian_basis(n) )
+ sage: B = _complex_hermitian_basis(n, QQ)
+ sage: all( M.is_symmetric() for M in B)
True
"""
return tuple(S)
-def _quaternion_hermitian_basis(n, field=QQ):
+def _quaternion_hermitian_basis(n, field):
"""
Returns a basis for the space of quaternion Hermitian n-by-n matrices.
sage: set_random_seed()
sage: n = ZZ.random_element(1,5)
- sage: all( M.is_symmetric() for M in _quaternion_hermitian_basis(n) )
+ sage: B = _quaternion_hermitian_basis(n, QQbar)
+ sage: all( M.is_symmetric() for M in B )
True
"""
Y_mat = Y.natural_representation()
return (X_mat*Y_mat).trace()
+def _real_symmetric_matrix_ip(X,Y):
+ return (X*Y).trace()
+
class RealSymmetricEJA(FiniteDimensionalEuclideanJordanAlgebra):
"""
sage: e0*e0
e0
sage: e1*e1
- e0 + e2
+ 1/2*e0 + 1/2*e2
sage: e2*e2
e2
sage: RealSymmetricEJA(3, prefix='q').gens()
(q0, q1, q2, q3, q4, q5)
+ Our inner product satisfies the Jordan axiom::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: J = RealSymmetricEJA(n)
+ sage: x = J.random_element()
+ sage: y = J.random_element()
+ sage: z = J.random_element()
+ sage: (x*y).inner_product(z) == y.inner_product(x*z)
+ True
+
+ Our basis is normalized with respect to the natural inner product::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: J = RealSymmetricEJA(n)
+ sage: all( b.norm() == 1 for b in J.gens() )
+ True
+
+ Left-multiplication operators are symmetric because they satisfy
+ the Jordan axiom::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: x = RealSymmetricEJA(n).random_element()
+ sage: x.operator().matrix().is_symmetric()
+ True
+
"""
def __init__(self, n, field=QQ, **kwargs):
- S = _real_symmetric_basis(n, field=field)
+ if n > 1 and field is QQ:
+ # 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.
+ field = QuadraticField(2, 'sqrt2')
+
+ S = _real_symmetric_basis(n, field)
Qs = _multiplication_table_from_matrix_basis(S)
fdeja = super(RealSymmetricEJA, self)
**kwargs)
def inner_product(self, x, y):
- return _matrix_ip(x,y)
+ X = x.natural_representation()
+ Y = y.natural_representation()
+ return _real_symmetric_matrix_ip(X,Y)
class ComplexHermitianEJA(FiniteDimensionalEuclideanJordanAlgebra):
sage: ComplexHermitianEJA(2, prefix='z').gens()
(z0, z1, z2, z3)
+ Our inner product satisfies the Jordan axiom::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: J = ComplexHermitianEJA(n)
+ sage: x = J.random_element()
+ sage: y = J.random_element()
+ sage: z = J.random_element()
+ sage: (x*y).inner_product(z) == y.inner_product(x*z)
+ True
+
"""
def __init__(self, n, field=QQ, **kwargs):
- S = _complex_hermitian_basis(n)
+ S = _complex_hermitian_basis(n, field)
Qs = _multiplication_table_from_matrix_basis(S)
fdeja = super(ComplexHermitianEJA, self)
sage: QuaternionHermitianEJA(2, prefix='a').gens()
(a0, a1, a2, a3, a4, a5)
+ Our inner product satisfies the Jordan axiom::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: J = QuaternionHermitianEJA(n)
+ sage: x = J.random_element()
+ sage: y = J.random_element()
+ sage: z = J.random_element()
+ sage: (x*y).inner_product(z) == y.inner_product(x*z)
+ True
+
"""
def __init__(self, n, field=QQ, **kwargs):
- S = _quaternion_hermitian_basis(n)
+ S = _quaternion_hermitian_basis(n, field)
Qs = _multiplication_table_from_matrix_basis(S)
fdeja = super(QuaternionHermitianEJA, self)
sage: JordanSpinEJA(2, prefix='B').gens()
(B0, B1)
+ Our inner product satisfies the Jordan axiom::
+
+ sage: set_random_seed()
+ sage: n = ZZ.random_element(1,5)
+ sage: J = JordanSpinEJA(n)
+ sage: x = J.random_element()
+ sage: y = J.random_element()
+ sage: z = J.random_element()
+ sage: (x*y).inner_product(z) == y.inner_product(x*z)
+ True
+
"""
def __init__(self, n, field=QQ, **kwargs):
V = VectorSpace(field, n)
projects / sage.d.git / blobdiff