1 from sage
.matrix
.constructor
import matrix
3 from mjo
.eja
.eja_algebra
import FiniteDimensionalEuclideanJordanAlgebra
4 from mjo
.eja
.eja_element
import FiniteDimensionalEuclideanJordanAlgebraElement
7 class FiniteDimensionalEuclideanJordanElementSubalgebraElement(FiniteDimensionalEuclideanJordanAlgebraElement
):
11 sage: from mjo.eja.eja_algebra import random_eja
15 The natural representation of an element in the subalgebra is
16 the same as its natural representation in the superalgebra::
18 sage: set_random_seed()
19 sage: A = random_eja().random_element().subalgebra_generated_by()
20 sage: y = A.random_element()
21 sage: actual = y.natural_representation()
22 sage: expected = y.superalgebra_element().natural_representation()
23 sage: actual == expected
28 def superalgebra_element(self
):
30 Return the object in our algebra's superalgebra that corresponds
35 sage: from mjo.eja.eja_algebra import (RealSymmetricEJA,
40 sage: J = RealSymmetricEJA(3)
41 sage: x = sum(J.gens())
43 e0 + e1 + e2 + e3 + e4 + e5
44 sage: A = x.subalgebra_generated_by()
47 sage: A(x).superalgebra_element()
48 e0 + e1 + e2 + e3 + e4 + e5
52 We can convert back and forth faithfully::
54 sage: set_random_seed()
55 sage: J = random_eja()
56 sage: x = J.random_element()
57 sage: A = x.subalgebra_generated_by()
58 sage: A(x).superalgebra_element() == x
60 sage: y = A.random_element()
61 sage: A(y.superalgebra_element()) == y
65 return self
.parent().superalgebra().linear_combination(
66 zip(self
.parent()._superalgebra
_basis
, self
.to_vector()) )
71 class FiniteDimensionalEuclideanJordanElementSubalgebra(FiniteDimensionalEuclideanJordanAlgebra
):
73 The subalgebra of an EJA generated by a single element.
75 def __init__(self
, elt
):
76 superalgebra
= elt
.parent()
78 # First compute the vector subspace spanned by the powers of
80 V
= superalgebra
.vector_space()
81 superalgebra_basis
= [superalgebra
.one()]
82 basis_vectors
= [superalgebra
.one().to_vector()]
83 W
= V
.span_of_basis(basis_vectors
)
84 for exponent
in range(1, V
.dimension()):
85 new_power
= elt
**exponent
86 basis_vectors
.append( new_power
.to_vector() )
88 W
= V
.span_of_basis(basis_vectors
)
89 superalgebra_basis
.append( new_power
)
91 # Vectors weren't independent; bail and keep the
92 # last subspace that worked.
95 # Make the basis hashable for UniqueRepresentation.
96 superalgebra_basis
= tuple(superalgebra_basis
)
98 # Now figure out the entries of the right-multiplication
99 # matrix for the successive basis elements b0, b1,... of
101 field
= superalgebra
.base_ring()
102 n
= len(superalgebra_basis
)
103 mult_table
= [[W
.zero() for i
in range(n
)] for j
in range(n
)]
106 product
= superalgebra_basis
[i
]*superalgebra_basis
[j
]
107 mult_table
[i
][j
] = W
.coordinate_vector(product
.to_vector())
109 # TODO: We'll have to redo this and make it unique again...
112 # The rank is the highest possible degree of a minimal
113 # polynomial, and is bounded above by the dimension. We know
114 # in this case that there's an element whose minimal
115 # polynomial has the same degree as the space's dimension
116 # (remember how we constructed the space?), so that must be
120 category
= superalgebra
.category().Associative()
121 natural_basis
= tuple( b
.natural_representation()
122 for b
in superalgebra_basis
)
124 self
._superalgebra
= superalgebra
125 self
._vector
_space
= W
126 self
._superalgebra
_basis
= superalgebra_basis
129 fdeja
= super(FiniteDimensionalEuclideanJordanElementSubalgebra
, self
)
130 return fdeja
.__init
__(field
,
135 natural_basis
=natural_basis
)
138 def _element_constructor_(self
, elt
):
140 Construct an element of this subalgebra from the given one.
141 The only valid arguments are elements of the parent algebra
142 that happen to live in this subalgebra.
146 sage: from mjo.eja.eja_algebra import RealSymmetricEJA
147 sage: from mjo.eja.eja_subalgebra import FiniteDimensionalEuclideanJordanElementSubalgebra
151 sage: J = RealSymmetricEJA(3)
152 sage: x = sum( i*J.gens()[i] for i in range(6) )
153 sage: K = FiniteDimensionalEuclideanJordanElementSubalgebra(x)
154 sage: [ K(x^k) for k in range(J.rank()) ]
160 if elt
in self
.superalgebra():
161 coords
= self
.vector_space().coordinate_vector(elt
.to_vector())
162 return self
.from_vector(coords
)
165 def superalgebra(self
):
167 Return the superalgebra that this algebra was generated from.
169 return self
._superalgebra
172 def vector_space(self
):
176 sage: from mjo.eja.eja_algebra import RealSymmetricEJA
177 sage: from mjo.eja.eja_subalgebra import FiniteDimensionalEuclideanJordanElementSubalgebra
181 sage: J = RealSymmetricEJA(3)
182 sage: x = sum( i*J.gens()[i] for i in range(6) )
183 sage: K = FiniteDimensionalEuclideanJordanElementSubalgebra(x)
184 sage: K.vector_space()
185 Vector space of degree 6 and dimension 3 over Rational Field
190 sage: (x^0).to_vector()
192 sage: (x^1).to_vector()
194 sage: (x^2).to_vector()
195 (10, 14, 21, 19, 31, 50)
198 return self
._vector
_space
201 Element
= FiniteDimensionalEuclideanJordanElementSubalgebraElement