Coxeter Types¶
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class
sage.combinat.root_system.coxeter_type.
CoxeterType
¶ Bases:
sage.structure.sage_object.SageObject
Abstract class for Coxeter types.
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bilinear_form
(R=None)¶ Return the bilinear form over
R
associated toself
.INPUT:
R
– (default: universal cyclotomic field) a ring used to compute the bilinear form
EXAMPLES:
sage: CoxeterType(['A', 2, 1]).bilinear_form() [ 1 -1/2 -1/2] [-1/2 1 -1/2] [-1/2 -1/2 1] sage: CoxeterType(['H', 3]).bilinear_form() [ 1 -1/2 0] [ -1/2 1 1/2*E(5)^2 + 1/2*E(5)^3] [ 0 1/2*E(5)^2 + 1/2*E(5)^3 1] sage: C = CoxeterMatrix([[1,-1,-1],[-1,1,-1],[-1,-1,1]]) sage: C.bilinear_form() [ 1 -1 -1] [-1 1 -1] [-1 -1 1]
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coxeter_graph
()¶ Return the Coxeter graph associated to
self
.EXAMPLES:
sage: CoxeterType(['A', 3]).coxeter_graph() Graph on 3 vertices sage: CoxeterType(['A', 3, 1]).coxeter_graph() Graph on 4 vertices
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coxeter_matrix
()¶ Return the Coxeter matrix associated to
self
.EXAMPLES:
sage: CoxeterType(['A', 3]).coxeter_matrix() [1 3 2] [3 1 3] [2 3 1] sage: CoxeterType(['A', 3, 1]).coxeter_matrix() [1 3 2 3] [3 1 3 2] [2 3 1 3] [3 2 3 1]
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index_set
()¶ Return the index set for
self
.This is the list of the nodes of the associated Coxeter graph.
EXAMPLES:
sage: CoxeterType(['A', 3, 1]).index_set() (0, 1, 2, 3) sage: CoxeterType(['D', 4]).index_set() (1, 2, 3, 4) sage: CoxeterType(['A', 7, 2]).index_set() (0, 1, 2, 3, 4) sage: CoxeterType(['A', 7, 2]).index_set() (0, 1, 2, 3, 4) sage: CoxeterType(['A', 6, 2]).index_set() (0, 1, 2, 3) sage: CoxeterType(['D', 6, 2]).index_set() (0, 1, 2, 3, 4, 5) sage: CoxeterType(['E', 6, 1]).index_set() (0, 1, 2, 3, 4, 5, 6) sage: CoxeterType(['E', 6, 2]).index_set() (0, 1, 2, 3, 4) sage: CoxeterType(['A', 2, 2]).index_set() (0, 1) sage: CoxeterType(['G', 2, 1]).index_set() (0, 1, 2) sage: CoxeterType(['F', 4, 1]).index_set() (0, 1, 2, 3, 4)
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is_affine
()¶ Return whether
self
is affine.EXAMPLES:
sage: CoxeterType(['A', 3]).is_affine() False sage: CoxeterType(['A', 3, 1]).is_affine() True
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is_crystallographic
()¶ Return whether
self
is crystallographic.This returns
False
by default. Derived class should override this appropriately.EXAMPLES:
sage: [ [t, t.is_crystallographic() ] for t in CartanType.samples(finite=True) ] [[['A', 1], True], [['A', 5], True], [['B', 1], True], [['B', 5], True], [['C', 1], True], [['C', 5], True], [['D', 2], True], [['D', 3], True], [['D', 5], True], [['E', 6], True], [['E', 7], True], [['E', 8], True], [['F', 4], True], [['G', 2], True], [['I', 5], False], [['H', 3], False], [['H', 4], False]]
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is_finite
()¶ Return whether
self
is finite.EXAMPLES:
sage: CoxeterType(['A',4]).is_finite() True sage: CoxeterType(['A',4, 1]).is_finite() False
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is_simply_laced
()¶ Return whether
self
is simply laced.This returns
False
by default. Derived class should override this appropriately.EXAMPLES:
sage: [ [t, t.is_simply_laced() ] for t in CartanType.samples() ] [[['A', 1], True], [['A', 5], True], [['B', 1], True], [['B', 5], False], [['C', 1], True], [['C', 5], False], [['D', 2], True], [['D', 3], True], [['D', 5], True], [['E', 6], True], [['E', 7], True], [['E', 8], True], [['F', 4], False], [['G', 2], False], [['I', 5], False], [['H', 3], False], [['H', 4], False], [['A', 1, 1], False], [['A', 5, 1], True], [['B', 1, 1], False], [['B', 5, 1], False], [['C', 1, 1], False], [['C', 5, 1], False], [['D', 3, 1], True], [['D', 5, 1], True], [['E', 6, 1], True], [['E', 7, 1], True], [['E', 8, 1], True], [['F', 4, 1], False], [['G', 2, 1], False], [['BC', 1, 2], False], [['BC', 5, 2], False], [['B', 5, 1]^*, False], [['C', 4, 1]^*, False], [['F', 4, 1]^*, False], [['G', 2, 1]^*, False], [['BC', 1, 2]^*, False], [['BC', 5, 2]^*, False]]
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rank
()¶ Return the rank of
self
.This is the number of nodes of the associated Coxeter graph.
EXAMPLES:
sage: CoxeterType(['A', 4]).rank() 4 sage: CoxeterType(['A', 7, 2]).rank() 5 sage: CoxeterType(['I', 8]).rank() 2
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classmethod
samples
(finite=None, affine=None, crystallographic=None)¶ Return a sample of the available Coxeter types.
INPUT:
finite
– a boolean orNone
(default:None
)affine
– a boolean orNone
(default:None
)crystallographic
– a boolean orNone
(default:None
)
The sample contains all the exceptional finite and affine Coxeter types, as well as typical representatives of the infinite families.
EXAMPLES:
sage: CoxeterType.samples() [Coxeter type of ['A', 1], Coxeter type of ['A', 5], Coxeter type of ['B', 1], Coxeter type of ['B', 5], Coxeter type of ['C', 1], Coxeter type of ['C', 5], Coxeter type of ['D', 4], Coxeter type of ['D', 5], Coxeter type of ['E', 6], Coxeter type of ['E', 7], Coxeter type of ['E', 8], Coxeter type of ['F', 4], Coxeter type of ['H', 3], Coxeter type of ['H', 4], Coxeter type of ['I', 10], Coxeter type of ['A', 2, 1], Coxeter type of ['B', 5, 1], Coxeter type of ['C', 5, 1], Coxeter type of ['D', 5, 1], Coxeter type of ['E', 6, 1], Coxeter type of ['E', 7, 1], Coxeter type of ['E', 8, 1], Coxeter type of ['F', 4, 1], Coxeter type of ['G', 2, 1], Coxeter type of ['A', 1, 1]]
The finite, affine and crystallographic options allow respectively for restricting to (non) finite, (non) affine, and (non) crystallographic Cartan types:
sage: CoxeterType.samples(finite=True) [Coxeter type of ['A', 1], Coxeter type of ['A', 5], Coxeter type of ['B', 1], Coxeter type of ['B', 5], Coxeter type of ['C', 1], Coxeter type of ['C', 5], Coxeter type of ['D', 4], Coxeter type of ['D', 5], Coxeter type of ['E', 6], Coxeter type of ['E', 7], Coxeter type of ['E', 8], Coxeter type of ['F', 4], Coxeter type of ['H', 3], Coxeter type of ['H', 4], Coxeter type of ['I', 10]] sage: CoxeterType.samples(affine=True) [Coxeter type of ['A', 2, 1], Coxeter type of ['B', 5, 1], Coxeter type of ['C', 5, 1], Coxeter type of ['D', 5, 1], Coxeter type of ['E', 6, 1], Coxeter type of ['E', 7, 1], Coxeter type of ['E', 8, 1], Coxeter type of ['F', 4, 1], Coxeter type of ['G', 2, 1], Coxeter type of ['A', 1, 1]] sage: CoxeterType.samples(crystallographic=True) [Coxeter type of ['A', 1], Coxeter type of ['A', 5], Coxeter type of ['B', 1], Coxeter type of ['B', 5], Coxeter type of ['C', 1], Coxeter type of ['C', 5], Coxeter type of ['D', 4], Coxeter type of ['D', 5], Coxeter type of ['E', 6], Coxeter type of ['E', 7], Coxeter type of ['E', 8], Coxeter type of ['F', 4], Coxeter type of ['A', 2, 1], Coxeter type of ['B', 5, 1], Coxeter type of ['C', 5, 1], Coxeter type of ['D', 5, 1], Coxeter type of ['E', 6, 1], Coxeter type of ['E', 7, 1], Coxeter type of ['E', 8, 1], Coxeter type of ['F', 4, 1], Coxeter type of ['G', 2, 1], Coxeter type of ['A', 1, 1]] sage: CoxeterType.samples(crystallographic=False) [Coxeter type of ['H', 3], Coxeter type of ['H', 4], Coxeter type of ['I', 10]]
Todo
add some reducible Coxeter types (suggestions?)
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class
sage.combinat.root_system.coxeter_type.
CoxeterTypeFromCartanType
(cartan_type)¶ Bases:
sage.structure.unique_representation.UniqueRepresentation
,sage.combinat.root_system.coxeter_type.CoxeterType
A Coxeter type associated to a Cartan type.
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cartan_type
()¶ Return the Cartan type used to construct
self
.EXAMPLES:
sage: C = CoxeterType(['C',3]) sage: C.cartan_type() ['C', 3]
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component_types
()¶ A list of Coxeter types making up the reducible type.
EXAMPLES:
sage: CoxeterType(['A',2],['B',2]).component_types() [Coxeter type of ['A', 2], Coxeter type of ['B', 2]] sage: CoxeterType('A4xB3').component_types() [Coxeter type of ['A', 4], Coxeter type of ['B', 3]] sage: CoxeterType(['A', 2]).component_types() Traceback (most recent call last): ... ValueError: component types only defined for reducible types
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coxeter_graph
()¶ Return the Coxeter graph of
self
.EXAMPLES:
sage: C = CoxeterType(['H',3]) sage: C.coxeter_graph().edges() [(1, 2, 3), (2, 3, 5)]
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coxeter_matrix
()¶ Return the Coxeter matrix associated to
self
.EXAMPLES:
sage: C = CoxeterType(['H',3]) sage: C.coxeter_matrix() [1 3 2] [3 1 5] [2 5 1]
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index_set
()¶ Return the index set of
self
.EXAMPLES:
sage: C = CoxeterType(['A', 4]) sage: C.index_set() (1, 2, 3, 4)
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is_affine
()¶ Return if
self
is an affine type.EXAMPLES:
sage: C = CoxeterType(['F', 4, 1]) sage: C.is_affine() True
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is_crystallographic
()¶ Return if
self
is crystallographic.EXAMPLES:
sage: C = CoxeterType(['C', 3]) sage: C.is_crystallographic() True sage: C = CoxeterType(['H', 3]) sage: C.is_crystallographic() False
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is_finite
()¶ Return if
self
is a finite type.EXAMPLES:
sage: C = CoxeterType(['E', 6]) sage: C.is_finite() True
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is_irreducible
()¶ Return if
self
is irreducible.EXAMPLES:
sage: C = CoxeterType(['A', 5]) sage: C.is_irreducible() True sage: C = CoxeterType('B3xB3') sage: C.is_irreducible() False
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is_reducible
()¶ Return if
self
is reducible.EXAMPLES:
sage: C = CoxeterType(['A', 5]) sage: C.is_reducible() False sage: C = CoxeterType('A2xA2') sage: C.is_reducible() True
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is_simply_laced
()¶ Return if
self
is simply-laced.EXAMPLES:
sage: C = CoxeterType(['A', 5]) sage: C.is_simply_laced() True sage: C = CoxeterType(['B', 3]) sage: C.is_simply_laced() False
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rank
()¶ Return the rank of
self
.EXAMPLES:
sage: C = CoxeterType(['I', 16]) sage: C.rank() 2
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relabel
(relabelling)¶ Return a relabelled copy of
self
.EXAMPLES:
sage: ct = CoxeterType(['A',2]) sage: ct.relabel({1:-1, 2:-2}) Coxeter type of ['A', 2] relabelled by {1: -1, 2: -2}
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type
()¶ Return the type of
self
.EXAMPLES:
sage: C = CoxeterType(['A', 4]) sage: C.type() 'A'
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