def affine_transformations_line(R, names=['X', 'Y'], representation='bracket'):
"""
The Lie algebra of affine transformations of the line.
EXAMPLES::
sage: L = lie_algebras.affine_transformations_line(QQ)
sage: L.structure_coefficients()
Finite family {('X', 'Y'): Y}
sage: X, Y = L.lie_algebra_generators()
sage: L[X, Y] == Y
True
sage: TestSuite(L).run()
sage: L = lie_algebras.affine_transformations_line(QQ, representation="matrix")
sage: X, Y = L.lie_algebra_generators()
sage: L[X, Y] == Y
True
sage: TestSuite(L).run()
"""
if isinstance(names, str):
names = names.split(',')
names = tuple(names)
if representation == 'matrix':
from sage.matrix.matrix_space import MatrixSpace
MS = MatrixSpace(R, 2, sparse=True)
one = R.one()
gens = tuple(MS({(0, i): one}) for i in range(2))
from sage.algebras.lie_algebras.lie_algebra import LieAlgebraFromAssociative
return LieAlgebraFromAssociative(MS, gens, names=names)
X = names[0]
Y = names[1]
from sage.algebras.lie_algebras.structure_coefficients import LieAlgebraWithStructureCoefficients
s_coeff = {(X, Y): {Y: R.one()}}
L = LieAlgebraWithStructureCoefficients(R, s_coeff, names=names)
L.rename(
"Lie algebra of affine transformations of a line over {}".format(R))
return L
def affine_transformations_line(R, names=['X', 'Y'], representation='bracket'):
"""
The Lie algebra of affine transformations of the line.
EXAMPLES::
sage: L = lie_algebras.affine_transformations_line(QQ)
sage: L.structure_coefficients()
Finite family {('X', 'Y'): Y}
sage: X, Y = L.lie_algebra_generators()
sage: L[X, Y] == Y
True
sage: TestSuite(L).run()
sage: L = lie_algebras.affine_transformations_line(QQ, representation="matrix")
sage: X, Y = L.lie_algebra_generators()
sage: L[X, Y] == Y
True
sage: TestSuite(L).run()
"""
if isinstance(names, str):
names = names.split(',')
names = tuple(names)
if representation == 'matrix':
from sage.matrix.matrix_space import MatrixSpace
MS = MatrixSpace(R, 2, sparse=True)
one = R.one()
gens = tuple(MS({(0,i):one}) for i in range(2))
from sage.algebras.lie_algebras.lie_algebra import LieAlgebraFromAssociative
return LieAlgebraFromAssociative(MS, gens, names=names)
X = names[0]
Y = names[1]
from sage.algebras.lie_algebras.structure_coefficients import LieAlgebraWithStructureCoefficients
s_coeff = {(X,Y): {Y:R.one()}}
L = LieAlgebraWithStructureCoefficients(R, s_coeff, names=names)
L.rename("Lie algebra of affine transformations of a line over {}".format(R))
return L
def three_dimensional_by_rank(R, n, a=None, names=['X', 'Y', 'Z']):
r"""
Return a 3-dimensional Lie algebra of rank ``n``, where `0 \leq n \leq 3`.
Here, the *rank* of a Lie algebra `L` is defined as the dimension
of its derived subalgebra `[L, L]`. (We are assuming that `R` is
a field of characteristic `0`; otherwise the Lie algebras
constructed by this function are still well-defined but no longer
might have the correct ranks.) This is not to be confused with
the other standard definition of a rank (namely, as the
dimension of a Cartan subalgebra, when `L` is semisimple).
INPUT:
- ``R`` -- the base ring
- ``n`` -- the rank
- ``a`` -- the deformation parameter (used for `n = 2`); this should
be a nonzero element of `R` in order for the resulting Lie
algebra to actually have the right rank(?)
- ``names`` -- (optional) the generator names
EXAMPLES::
sage: lie_algebras.three_dimensional_by_rank(QQ, 0)
Abelian Lie algebra on 3 generators (X, Y, Z) over Rational Field
sage: L = lie_algebras.three_dimensional_by_rank(QQ, 1)
sage: L.structure_coefficients()
Finite family {('Y', 'Z'): X}
sage: L = lie_algebras.three_dimensional_by_rank(QQ, 2, 4)
sage: L.structure_coefficients()
Finite family {('X', 'Y'): Y, ('X', 'Z'): Y + Z}
sage: L = lie_algebras.three_dimensional_by_rank(QQ, 2, 0)
sage: L.structure_coefficients()
Finite family {('X', 'Y'): Y}
sage: lie_algebras.three_dimensional_by_rank(QQ, 3)
sl2 over Rational Field
"""
if isinstance(names, str):
names = names.split(',')
names = tuple(names)
if n == 0:
from sage.algebras.lie_algebras.abelian import AbelianLieAlgebra
return AbelianLieAlgebra(R, names=names)
if n == 1:
L = three_dimensional(R, 0, 1, 0, 0, names=names) # Strictly upper triangular matrices
L.rename("Lie algebra of 3x3 strictly upper triangular matrices over {}".format(R))
return L
if n == 2:
if a is None:
raise ValueError("The parameter 'a' must be specified")
X = names[0]
Y = names[1]
Z = names[2]
from sage.algebras.lie_algebras.structure_coefficients import LieAlgebraWithStructureCoefficients
if a == 0:
s_coeff = {(X,Y): {Y:R.one()}, (X,Z): {Y:R(a)}}
# Why use R(a) here if R == 0 ? Also this has rank 1.
L = LieAlgebraWithStructureCoefficients(R, s_coeff, tuple(names))
L.rename("Degenerate Lie algebra of dimension 3 and rank 2 over {}".format(R))
else:
s_coeff = {(X,Y): {Y:R.one()}, (X,Z): {Y:R.one(), Z:R.one()}}
# a doesn't appear here :/
L = LieAlgebraWithStructureCoefficients(R, s_coeff, tuple(names))
L.rename("Lie algebra of dimension 3 and rank 2 with parameter {} over {}".format(a, R))
return L
if n == 3:
#return sl(R, 2)
from sage.algebras.lie_algebras.structure_coefficients import LieAlgebraWithStructureCoefficients
E = names[0]
F = names[1]
H = names[2]
s_coeff = { (E,F): {H:R.one()}, (H,E): {E:R(2)}, (H,F): {F:R(-2)} }
L = LieAlgebraWithStructureCoefficients(R, s_coeff, tuple(names))
L.rename("sl2 over {}".format(R))
return L
raise ValueError("Invalid rank")
def three_dimensional_by_rank(R, n, a=None, names=['X', 'Y', 'Z']):
"""
Return a 3-dimensional Lie algebra of rank ``n``, where `0 \leq n \leq 3`.
Here, the *rank* of a Lie algebra `L` is defined as the dimension
of its derived subalgebra `[L, L]`. (We are assuming that `R` is
a field of characteristic `0`; otherwise the Lie algebras
constructed by this function are still well-defined but no longer
might have the correct ranks.) This is not to be confused with
the other standard definition of a rank (namely, as the
dimension of a Cartan subalgebra, when `L` is semisimple).
INPUT:
- ``R`` -- the base ring
- ``n`` -- the rank
- ``a`` -- the deformation parameter (used for `n = 2`); this should
be a nonzero element of `R` in order for the resulting Lie
algebra to actually have the right rank(?)
- ``names`` -- (optional) the generator names
EXAMPLES::
sage: lie_algebras.three_dimensional_by_rank(QQ, 0)
Abelian Lie algebra on 3 generators (X, Y, Z) over Rational Field
sage: L = lie_algebras.three_dimensional_by_rank(QQ, 1)
sage: L.structure_coefficients()
Finite family {('Y', 'Z'): X}
sage: L = lie_algebras.three_dimensional_by_rank(QQ, 2, 4)
sage: L.structure_coefficients()
Finite family {('X', 'Y'): Y, ('X', 'Z'): Y + Z}
sage: L = lie_algebras.three_dimensional_by_rank(QQ, 2, 0)
sage: L.structure_coefficients()
Finite family {('X', 'Y'): Y}
sage: lie_algebras.three_dimensional_by_rank(QQ, 3)
sl2 over Rational Field
"""
if isinstance(names, str):
names = names.split(',')
names = tuple(names)
if n == 0:
from sage.algebras.lie_algebras.abelian import AbelianLieAlgebra
return AbelianLieAlgebra(R, names=names)
if n == 1:
L = three_dimensional(R, 0, 1, 0, 0, names=names) # Strictly upper triangular matrices
L.rename("Lie algebra of 3x3 strictly upper triangular matrices over {}".format(R))
return L
if n == 2:
if a is None:
raise ValueError("The parameter 'a' must be specified")
X = names[0]
Y = names[1]
Z = names[2]
from sage.algebras.lie_algebras.structure_coefficients import LieAlgebraWithStructureCoefficients
if a == 0:
s_coeff = {(X,Y): {Y:R.one()}, (X,Z): {Y:R(a)}}
# Why use R(a) here if R == 0 ? Also this has rank 1.
L = LieAlgebraWithStructureCoefficients(R, s_coeff, tuple(names))
L.rename("Degenerate Lie algebra of dimension 3 and rank 2 over {}".format(R))
else:
s_coeff = {(X,Y): {Y:R.one()}, (X,Z): {Y:R.one(), Z:R.one()}}
# a doesn't appear here :/
L = LieAlgebraWithStructureCoefficients(R, s_coeff, tuple(names))
L.rename("Lie algebra of dimension 3 and rank 2 with parameter {} over {}".format(a, R))
return L
if n == 3:
#return sl(R, 2)
from sage.algebras.lie_algebras.structure_coefficients import LieAlgebraWithStructureCoefficients
E = names[0]
F = names[1]
H = names[2]
s_coeff = { (E,F): {H:R.one()}, (H,E): {E:R(2)}, (H,F): {F:R(-2)} }
L = LieAlgebraWithStructureCoefficients(R, s_coeff, tuple(names))
L.rename("sl2 over {}".format(R))
return L
raise ValueError("Invalid rank")
