# Kac-Moody Algebras With Triangular Decomposition Basis¶

AUTHORS:

• Travis Scrimshaw (07-15-2017): Initial implementation
class sage.categories.triangular_kac_moody_algebras.TriangularKacMoodyAlgebras(base, name=None)

Category of Kac-Moody algebras with a distinguished basis that respects the triangular decomposition.

We require that the grading group is the root lattice of the appropriate Cartan type.

class ElementMethods

Bases: object

part()

Return whether the element v is in the lower, zero, or upper part of self.

OUTPUT:

$$-1$$ if v is in the lower part, $$0$$ if in the zero part, or $$1$$ if in the upper part

EXAMPLES:

sage: L = LieAlgebra(QQ, cartan_type="F4")
sage: L.inject_variables()
Defining e1, e2, e3, e4, f1, f2, f3, f4, h1, h2, h3, h4
sage: e1.part()
1
sage: f4.part()
-1
sage: (h2 + h3).part()
0
sage: (f1.bracket(f2) + 4*f4).part()
-1
sage: (e1 + f1).part()
Traceback (most recent call last):
...
ValueError: element is not in one part

class ParentMethods

Bases: object

e(i=None)

Return the generators $$e$$ of self.

INPUT:

• i – (optional) if specified, return just the generator $$e_i$$

EXAMPLES:

sage: L = lie_algebras.so(QQ, 5)
sage: L.e()
Finite family {1: E[alpha[1]], 2: E[alpha[2]]}
sage: L.e(1)
E[alpha[1]]

f(i=None)

Return the generators $$f$$ of self.

INPUT:

• i – (optional) if specified, return just the generator $$f_i$$

EXAMPLES:

sage: L = lie_algebras.so(QQ, 5)
sage: L.f()
Finite family {1: E[-alpha[1]], 2: E[-alpha[2]]}
sage: L.f(1)
E[-alpha[1]]

verma_module(la, basis_key=None, **kwds)

Return the Verma module with highest weight la over self.

INPUT:

• basis_key – (optional) a key function for the indexing set of the basis elements of self

EXAMPLES:

sage: L = lie_algebras.sl(QQ, 3)
sage: P = L.cartan_type().root_system().weight_lattice()
sage: La = P.fundamental_weights()
sage: M = L.verma_module(La[1]+La[2])
sage: M
Verma module with highest weight Lambda[1] + Lambda[2]
of Lie algebra of ['A', 2] in the Chevalley basis

super_categories()

EXAMPLES:

sage: from sage.categories.triangular_kac_moody_algebras import TriangularKacMoodyAlgebras
sage: TriangularKacMoodyAlgebras(QQ).super_categories()
[Join of Category of graded lie algebras with basis over Rational Field
and Category of kac moody algebras over Rational Field]