def rho(self):
r"""
Return the vertex ``rho`` of the basic hyperbolic
triangle which describes ``self``. ``rho`` has
absolute value 1 and angle ``pi/n``.
EXAMPLES::
sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
sage: HeckeTriangleGroup(3).rho() == 1/2 + sqrt(3)/2*i
True
sage: HeckeTriangleGroup(4).rho() == sqrt(2)/2*(1 + i)
True
sage: HeckeTriangleGroup(6).rho() == sqrt(3)/2 + 1/2*i
True
sage: HeckeTriangleGroup(10).rho()
0.95105651629515...? + 0.30901699437494...?*I
sage: HeckeTriangleGroup(infinity).rho()
1
"""
# TODO: maybe rho should be replaced by -rhobar
# Also we could use NumberFields...
if (self._n == infinity):
return coerce_AA(1)
else:
rho = AlgebraicField()(exp(pi/self._n*i))
rho.simplify()
return rho
def rho(self):
r"""
Return the vertex ``rho`` of the basic hyperbolic
triangle which describes ``self``. ``rho`` has
absolute value 1 and angle ``pi/n``.
EXAMPLES::
sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
sage: HeckeTriangleGroup(3).rho() == QQbar(1/2 + sqrt(3)/2*i)
True
sage: HeckeTriangleGroup(4).rho() == QQbar(sqrt(2)/2*(1 + i))
True
sage: HeckeTriangleGroup(6).rho() == QQbar(sqrt(3)/2 + 1/2*i)
True
sage: HeckeTriangleGroup(10).rho()
0.95105651629515...? + 0.30901699437494...?*I
sage: HeckeTriangleGroup(infinity).rho()
1
"""
# TODO: maybe rho should be replaced by -rhobar
# Also we could use NumberFields...
if (self._n == infinity):
return coerce_AA(1)
else:
rho = AlgebraicField()(exp(pi / self._n * i))
rho.simplify()
return rho
def root_extension_embedding(self, D, K=None):
r"""
Return the correct embedding from the root extension field
of the given discriminant ``D`` to the field ``K``.
Also see the method ``root_extension_embedding(K)`` of
``HeckeTriangleGroupElement`` for more examples.
INPUT:
- ``D`` -- An element of the base ring of ``self``
corresponding to a discriminant.
- ``K`` -- A field to which we want the (correct) embeddding.
If ``K=None`` (default) then ``AlgebraicField()`` is
used for positive ``D`` and ``AlgebraicRealField()``
otherwise.
OUTPUT:
The corresponding embedding if it was found.
Otherwise a ValueError is raised.
EXAMPLES::
sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
sage: G = HeckeTriangleGroup(n=infinity)
sage: G.root_extension_embedding(32)
Ring morphism:
From: Number Field in e with defining polynomial x^2 - 32
To: Algebraic Real Field
Defn: e |--> 5.656854249492...?
sage: G.root_extension_embedding(-4)
Ring morphism:
From: Number Field in e with defining polynomial x^2 + 4
To: Algebraic Field
Defn: e |--> 2*I
sage: G.root_extension_embedding(4)
Coercion map:
From: Rational Field
To: Algebraic Real Field
sage: G = HeckeTriangleGroup(n=7)
sage: lam = G.lam()
sage: D = 4*lam^2 + 4*lam - 4
sage: G.root_extension_embedding(D, CC)
Relative number field morphism:
From: Number Field in e with defining polynomial x^2 - 4*lam^2 - 4*lam + 4 over its base field
To: Complex Field with 53 bits of precision
Defn: e |--> 4.02438434522...
lam |--> 1.80193773580...
sage: D = lam^2 - 4
sage: G.root_extension_embedding(D)
Relative number field morphism:
From: Number Field in e with defining polynomial x^2 - lam^2 + 4 over its base field
To: Algebraic Field
Defn: e |--> 0.?... + 0.867767478235...?*I
lam |--> 1.801937735804...?
"""
D = self.base_ring()(D)
F = self.root_extension_field(D)
if K is None:
if coerce_AA(D) > 0:
K = AA
else:
K = AlgebraicField()
L = [emb for emb in F.embeddings(K)]
# Three possibilities up to numerical artefacts:
# (1) emb = e, purely imaginary
# (2) emb = e or lam (can't distinguish), purely real
# (3) emb = (e,lam), e purely imaginary, lam purely real
# (4) emb = (e,lam), e purely real, lam purely real
# There always exists one emb with "e" positive resp. positive imaginary
# and if there is a lam there exists a positive one...
#
# Criteria to pick the correct "maximum":
# 1. First figure out if e resp. lam is purely real or imaginary
# (using "abs(e.imag()) > abs(e.real())")
# 2. In the purely imaginary case we don't want anything negative imaginary
# and we know the positive case is unique after sorting lam
# 3. For the remaining cases we want the biggest real part
# (and lam should get comparison priority)
def emb_key(emb):
L = []
gens_len = len(emb.im_gens())
for k in range(gens_len):
a = emb.im_gens()[k]
try:
a.simplify()
a.exactify()
except AttributeError:
pass
# If a is purely imaginary:
if abs(a.imag()) > abs(a.real()):
if a.imag() < 0:
a = -infinity
else:
a = ZZ(0)
else:
a = a.real()
L.append(a)
L.reverse()
return L
if len(L) > 1:
L.sort(key=emb_key)
return L[-1]
def root_extension_embedding(self, K=AlgebraicField()):
r"""
Return the correct embedding from the root extension field to ``K`` (default: ``AlgebraicField()``).
EXAMPLES::
sage: from sage.modular.modform_hecketriangle.hecke_triangle_groups import HeckeTriangleGroup
sage: G = HeckeTriangleGroup(n=infinity)
sage: fp = (-G.S()).fixed_points()[0]
sage: alg_fp = (-G.S()).root_extension_embedding()(fp)
sage: alg_fp
1*I
sage: alg_fp == (-G.S()).fixed_points(embedded=True)[0]
True
sage: fp = (-G.V(2)).fixed_points()[1]
sage: alg_fp = (-G.V(2)).root_extension_embedding(AA)(fp)
sage: alg_fp
-1.732050807568...?
sage: alg_fp == (-G.V(2)).fixed_points(embedded=True)[1]
True
sage: fp = (-G.V(2)).fixed_points()[0]
sage: alg_fp = (-G.V(2)).root_extension_embedding(AA)(fp)
sage: alg_fp
1.732050807568...?
sage: alg_fp == (-G.V(2)).fixed_points(embedded=True)[0]
True
sage: G = HeckeTriangleGroup(n=7)
sage: fp = (-G.S()).fixed_points()[1]
sage: alg_fp = (-G.S()).root_extension_embedding()(fp)
sage: alg_fp
0.?... - 1.000000000000...?*I
sage: alg_fp == (-G.S()).fixed_points(embedded=True)[1]
True
sage: fp = (-G.U()^4).fixed_points()[0]
sage: alg_fp = (-G.U()^4).root_extension_embedding()(fp)
sage: alg_fp
0.9009688679024...? + 0.4338837391175...?*I
sage: alg_fp == (-G.U()^4).fixed_points(embedded=True)[0]
True
sage: (-G.U()^4).root_extension_embedding(CC)(fp)
0.900968867902... + 0.433883739117...*I
sage: (-G.U()^4).root_extension_embedding(CC)(fp).parent()
Complex Field with 53 bits of precision
sage: fp = (-G.V(5)).fixed_points()[1]
sage: alg_fp = (-G.V(5)).root_extension_embedding(AA)(fp)
sage: alg_fp
-0.6671145837954...?
sage: alg_fp == (-G.V(5)).fixed_points(embedded=True)[1]
True
"""
G = self.parent()
D = self.discriminant()
F = self.root_extension_field()
n = G.n()
if D.is_square():
e = D.sqrt()
lam = G.lam()
elif n in [3, infinity]:
e = F.gen(0)
lam = G.lam()
else:
(e, lam) = F.gens()
emb_lam = K(G.lam())
if self.is_elliptic():
emb_e = K(AlgebraicField()(D).sqrt())
else:
emb_e = K(AA(D).sqrt())
guess = ZZ(0)
min_value = infinity
index = ZZ(0)
for (index,
emb) in enumerate(self.root_extension_field().embeddings(K)):
if K.is_exact():
if emb(lam) == emb_lam and emb(e) == emb_e:
return emb
else:
value = (emb(lam) - emb_lam).n(
K.prec()).abs() + (emb(e) - emb_e).n(K.prec()).abs()
if (value < min_value):
guess = index
min_value = value
if K.is_exact() or min_value == infinity:
raise ValueError(
"No suitable embedding is available for K = {}!".format(K))
else:
return self.root_extension_field().embeddings(K)[guess]
