def can_convert_to_singular(R):
"""
Returns True if this ring's base field or ring can be
represented in Singular, and the polynomial ring has at
least one generator. If this is True then this polynomial
ring can be represented in Singular.
The following base rings are supported: finite fields, rationals, number
fields, and real and complex fields.
EXAMPLES::
sage: from sage.rings.polynomial.polynomial_singular_interface import can_convert_to_singular
sage: can_convert_to_singular(PolynomialRing(QQ, names=['x']))
True
sage: can_convert_to_singular(PolynomialRing(QQ, names=[]))
False
"""
if R.ngens() == 0:
return False;
base_ring = R.base_ring()
return ( sage.rings.finite_rings.constructor.is_FiniteField(base_ring)
or is_RationalField(base_ring)
or (base_ring.is_prime_field() and base_ring.characteristic() <= 2147483647)
or is_RealField(base_ring)
or is_ComplexField(base_ring)
or is_RealDoubleField(base_ring)
or is_ComplexDoubleField(base_ring)
or number_field.all.is_NumberField(base_ring)
or ( sage.rings.fraction_field.is_FractionField(base_ring) and ( base_ring.base_ring().is_prime_field() or base_ring.base_ring() is ZZ ) )
or base_ring is ZZ
or is_IntegerModRing(base_ring) )
def can_convert_to_singular(R):
"""
Returns True if this ring's base field or ring can be
represented in Singular, and the polynomial ring has at
least one generator. If this is True then this polynomial
ring can be represented in Singular.
The following base rings are supported: finite fields, rationals, number
fields, and real and complex fields.
EXAMPLES::
sage: from sage.rings.polynomial.polynomial_singular_interface import can_convert_to_singular
sage: can_convert_to_singular(PolynomialRing(QQ, names=['x']))
True
sage: can_convert_to_singular(PolynomialRing(QQ, names=[]))
False
"""
if R.ngens() == 0:
return False;
base_ring = R.base_ring()
return ( sage.rings.finite_rings.constructor.is_FiniteField(base_ring)
or is_RationalField(base_ring)
or (base_ring.is_prime_field() and base_ring.characteristic() <= 2147483647)
or is_RealField(base_ring)
or is_ComplexField(base_ring)
or is_RealDoubleField(base_ring)
or is_ComplexDoubleField(base_ring)
or number_field.all.is_NumberField(base_ring)
or ( sage.rings.fraction_field.is_FractionField(base_ring) and ( base_ring.base_ring().is_prime_field() or base_ring.base_ring() is ZZ ) )
or base_ring is ZZ
or is_IntegerModRing(base_ring) )
def schmidt_t5_eigenvalue_numerical(self, t):
(tau1, z, tau2) = t
from sage.libs.mpmath import mp
from sage.libs.mpmath.mp import exp, pi
from sage.libs.mpmath.mp import j as i
if not Integer(self.__level()).is_prime():
raise ValueError("T_5 is only unique if the level is a prime")
precision = ParamodularFormD2Filter_trace(self.precision())
s = Sequence([tau1, z, tau2])
if not is_ComplexField(s):
mp_precision = 30
else:
mp_precision = ceil(3.33 * s.universe().precision())
mp.dps = mp_precision
p1list = P1List(self.level())
## Prepare the operation for d_1(N)
## We have to invert the lifts since we will later use apply_GL_to_form
d1_matrices = [p1list.lift_to_sl2z(i) for i in range(len(p1list))]
d1_matrices = [(a_b_c_d[3], -a_b_c_d[1], -a_b_c_d[2], a_b_c_d[0])
for a_b_c_d in d1_matrices]
## Prepare the evaluation points corresponding to d_02(N)
d2_points = list()
for i in range(len(p1list())):
(a, b, c, d) = p1list.lift_to_sl2z(i)
tau1p = (a * tau1 + b) / (c * tau1 + d)
zp = z / (c * tau1 + d)
tau2p = tau2 - c * z**2 / (c * tau1 + d)
(e_tau1p, e_zp, e_tau2p) = (exp(2 * pi * i * tau1p),
exp(2 * pi * i * zp),
exp(2 * pi * i * tau2p))
d2_points.append((e_tau1p, e_zp, e_tau2p))
(e_tau1, e_z, e_tau2) = (exp(2 * pi * i * tau1), exp(2 * pi * i * z),
exp(2 * pi * i * tau2))
self_value = s.universe().zero()
trans_value = s.universe().zero()
for k in precision:
(a, b, c) = apply_GL_to_form(self._P1List()(k[1]), k[0])
self_value = self_value + self[k] * e_tau1**a * e_z**b * e_tau2**c
for m in d1_matrices:
(ap, bp, cp) = apply_GL_to_form(m, (a, b, c))
for (e_tau1p, e_zp, e_tau2p) in d2_points:
trans_value = trans_value + self[((
ap, bp, cp), 0)] * e_tau1p**ap * e_zp**bp * e_tau2p**cp
return trans_value / self_value
def _evalf_(self, n, x, **kwds):
"""
Evaluate :class:`chebyshev_U` numerically with mpmath.
EXAMPLES::
sage: chebyshev_U(5,-4+3.*I)
98280.0000000000 - 11310.0000000000*I
sage: chebyshev_U(10,3).n(75)
4.661117900000000000000e7
sage: chebyshev_U._evalf_(1.5, Mod(8,9))
Traceback (most recent call last):
...
TypeError: cannot evaluate chebyshev_U with parent Ring of integers modulo 9
"""
try:
real_parent = kwds['parent']
except KeyError:
real_parent = parent(x)
if not is_RealField(real_parent) and not is_ComplexField(
real_parent):
# parent is not a real or complex field: figure out a good parent
if x in RR:
x = RR(x)
real_parent = RR
elif x in CC:
x = CC(x)
real_parent = CC
if not is_RealField(real_parent) and not is_ComplexField(real_parent):
raise TypeError(
"cannot evaluate chebyshev_U with parent {}".format(
real_parent))
from sage.libs.mpmath.all import call as mpcall
from sage.libs.mpmath.all import chebyu as mpchebyu
return mpcall(mpchebyu, n, x, parent=real_parent)
def can_convert_to_singular(R):
"""
Returns True if this ring's base field or ring can be
represented in Singular, and the polynomial ring has at
least one generator. If this is True then this polynomial
ring can be represented in Singular.
The following base rings are supported: finite fields, rationals, number
fields, and real and complex fields.
EXAMPLES::
sage: from sage.rings.polynomial.polynomial_singular_interface import can_convert_to_singular
sage: can_convert_to_singular(PolynomialRing(QQ, names=['x']))
True
sage: can_convert_to_singular(PolynomialRing(QQ, names=[]))
False
TESTS:
Avoid non absolute number fields (see :trac:`23535`)::
sage: K.<a,b> = NumberField([x^2-2,x^2-5])
sage: can_convert_to_singular(K['s,t'])
False
"""
if R.ngens() == 0:
return False;
base_ring = R.base_ring()
if (base_ring is ZZ
or sage.rings.finite_rings.finite_field_constructor.is_FiniteField(base_ring)
or is_RationalField(base_ring)
or is_IntegerModRing(base_ring)
or is_RealField(base_ring)
or is_ComplexField(base_ring)
or is_RealDoubleField(base_ring)
or is_ComplexDoubleField(base_ring)):
return True
elif base_ring.is_prime_field():
return base_ring.characteristic() <= 2147483647
elif number_field.number_field_base.is_NumberField(base_ring):
return base_ring.is_absolute()
elif sage.rings.fraction_field.is_FractionField(base_ring):
B = base_ring.base_ring()
return B.is_prime_field() or B is ZZ or is_FiniteField(B)
elif is_RationalFunctionField(base_ring):
return base_ring.constant_field().is_prime_field()
else:
return False
def elliptic_j(z):
r"""
Returns the elliptic modular `j`-function evaluated at `z`.
INPUT:
- ``z`` (complex) -- a complex number with positive imaginary part.
OUTPUT:
(complex) The value of `j(z)`.
ALGORITHM:
Calls the ``pari`` function ``ellj()``.
AUTHOR:
John Cremona
EXAMPLES::
sage: elliptic_j(CC(i))
1728.00000000000
sage: elliptic_j(sqrt(-2.0))
8000.00000000000
sage: z = ComplexField(100)(1,sqrt(11))/2
sage: elliptic_j(z)
-32768.000...
sage: elliptic_j(z).real().round()
-32768
::
sage: tau = (1 + sqrt(-163))/2
sage: (-elliptic_j(tau.n(100)).real().round())^(1/3)
640320
"""
CC = z.parent()
from sage.rings.complex_field import is_ComplexField
if not is_ComplexField(CC):
CC = ComplexField()
try:
z = CC(z)
except ValueError:
raise ValueError("elliptic_j only defined for complex arguments.")
from sage.libs.all import pari
return CC(pari(z).ellj())
def can_convert_to_singular(R):
"""
Returns True if this ring's base field or ring can be
represented in Singular, and the polynomial ring has at
least one generator. If this is True then this polynomial
ring can be represented in Singular.
The following base rings are supported: finite fields, rationals, number
fields, and real and complex fields.
EXAMPLES::
sage: from sage.rings.polynomial.polynomial_singular_interface import can_convert_to_singular
sage: can_convert_to_singular(PolynomialRing(QQ, names=['x']))
True
sage: can_convert_to_singular(PolynomialRing(ZZ, names=['x']))
True
sage: can_convert_to_singular(PolynomialRing(QQ, names=[]))
False
TESTS:
Avoid non absolute number fields (see :trac:`23535`)::
sage: K.<a,b> = NumberField([x^2-2,x^2-5])
sage: can_convert_to_singular(K['s,t'])
False
"""
if R.ngens() == 0:
return False
base_ring = R.base_ring()
if (base_ring is ZZ
or sage.rings.finite_rings.finite_field_constructor.is_FiniteField(
base_ring) or is_RationalField(base_ring)
or is_IntegerModRing(base_ring) or is_RealField(base_ring)
or is_ComplexField(base_ring) or is_RealDoubleField(base_ring)
or is_ComplexDoubleField(base_ring)):
return True
elif base_ring.is_prime_field():
return base_ring.characteristic() <= 2147483647
elif number_field.number_field_base.is_NumberField(base_ring):
return base_ring.is_absolute()
elif sage.rings.fraction_field.is_FractionField(base_ring):
B = base_ring.base_ring()
return B.is_prime_field() or B is ZZ or is_FiniteField(B)
elif is_RationalFunctionField(base_ring):
return base_ring.constant_field().is_prime_field()
else:
return False
def elliptic_j(z):
r"""
Returns the elliptic modular `j`-function evaluated at `z`.
INPUT:
- ``z`` (complex) -- a complex number with positive imaginary part.
OUTPUT:
(complex) The value of `j(z)`.
ALGORITHM:
Calls the ``pari`` function ``ellj()``.
AUTHOR:
John Cremona
EXAMPLES::
sage: elliptic_j(CC(i))
1728.00000000000
sage: elliptic_j(sqrt(-2.0))
8000.00000000000
sage: z = ComplexField(100)(1,sqrt(11))/2
sage: elliptic_j(z)
-32768.000...
sage: elliptic_j(z).real().round()
-32768
::
sage: tau = (1 + sqrt(-163))/2
sage: (-elliptic_j(tau.n(100)).real().round())^(1/3)
640320
"""
CC = z.parent()
from sage.rings.complex_field import is_ComplexField
if not is_ComplexField(CC):
CC = ComplexField()
try:
z = CC(z)
except ValueError:
raise ValueError("elliptic_j only defined for complex arguments.")
from sage.libs.all import pari
return CC(pari(z).ellj())
def _evalf_(self, n, x, **kwds):
"""
Evaluate :class:`chebyshev_U` numerically with mpmath.
EXAMPLES::
sage: chebyshev_U(5,-4+3.*I)
98280.0000000000 - 11310.0000000000*I
sage: chebyshev_U(10,3).n(75)
4.661117900000000000000e7
sage: chebyshev_U._evalf_(1.5, Mod(8,9))
Traceback (most recent call last):
...
TypeError: cannot evaluate chebyshev_U with parent Ring of integers modulo 9
"""
try:
real_parent = kwds["parent"]
except KeyError:
real_parent = parent(x)
if not is_RealField(real_parent) and not is_ComplexField(real_parent):
# parent is not a real or complex field: figure out a good parent
if x in RR:
x = RR(x)
real_parent = RR
elif x in CC:
x = CC(x)
real_parent = CC
if not is_RealField(real_parent) and not is_ComplexField(real_parent):
raise TypeError("cannot evaluate chebyshev_U with parent {}".format(real_parent))
from sage.libs.mpmath.all import call as mpcall
from sage.libs.mpmath.all import chebyu as mpchebyu
return mpcall(mpchebyu, n, x, parent=real_parent)
def __call__(self, g):
"""
Evaluate ``self`` on a group element ``g``.
OUTPUT:
An element in
:meth:`~sage.groups.abelian_gps.dual_abelian_group.DualAbelianGroup_class.base_ring`.
EXAMPLES::
sage: F = AbelianGroup(5, [2,3,5,7,8], names="abcde")
sage: a,b,c,d,e = F.gens()
sage: Fd = F.dual_group(names="ABCDE")
sage: A,B,C,D,E = Fd.gens()
sage: A*B^2*D^7
A*B^2
sage: A(a)
-1
sage: B(b)
zeta840^140 - 1
sage: CC(B(b)) # abs tol 1e-8
-0.499999999999995 + 0.866025403784447*I
sage: A(a*b)
-1
"""
F = self.parent().base_ring()
expsX = self.exponents()
expsg = g.exponents()
order = self.parent().gens_orders()
N = LCM(order)
if is_ComplexField(F):
from sage.symbolic.constants import pi
I = F.gen()
PI = F(pi)
ans = prod([
exp(2 * PI * I * expsX[i] * expsg[i] / order[i])
for i in range(len(expsX))
])
return ans
ans = F(1) ## assumes F is the cyclotomic field
zeta = F.gen()
for i in range(len(expsX)):
order_noti = N / order[i]
ans = ans * zeta**(expsX[i] * expsg[i] * order_noti)
return ans
def __call__(self, g):
"""
Evaluate ``self`` on a group element ``g``.
OUTPUT:
An element in
:meth:`~sage.groups.abelian_gps.dual_abelian_group.DualAbelianGroup_class.base_ring`.
EXAMPLES::
sage: F = AbelianGroup(5, [2,3,5,7,8], names="abcde")
sage: a,b,c,d,e = F.gens()
sage: Fd = F.dual_group(names="ABCDE")
sage: A,B,C,D,E = Fd.gens()
sage: A*B^2*D^7
A*B^2
sage: A(a)
-1
sage: B(b)
zeta840^140 - 1
sage: CC(B(b)) # abs tol 1e-8
-0.499999999999995 + 0.866025403784447*I
sage: A(a*b)
-1
"""
F = self.parent().base_ring()
expsX = self.exponents()
expsg = g.exponents()
order = self.parent().gens_orders()
N = LCM(order)
if is_ComplexField(F):
from sage.symbolic.constants import pi
I = F.gen()
PI = F(pi)
ans = prod([(2*PI*I*expsX[i]*expsg[i]/order[i]).exp() for i in range(len(expsX))])
return ans
ans = F(1) ## assumes F is the cyclotomic field
zeta = F.gen()
for i in range(len(expsX)):
order_noti = N/order[i]
ans = ans*zeta**(expsX[i]*expsg[i]*order_noti)
return ans
def atkin_lehner_eigenvalue_numerical(self, t):
(tau1, z, tau2) = t
from sage.libs.mpmath import mp
from sage.libs.mpmath.mp import exp, pi
from sage.libs.mpmath.mp import j as i
if not Integer(self.__level()).is_prime():
raise ValueError(
"The Atkin Lehner involution is only unique if the level is a prime"
)
precision = ParamodularFormD2Filter_trace(self.precision())
s = Sequence([tau1, z, tau2])
if not is_ComplexField(s):
mp_precision = 30
else:
mp_precision = ceil(3.33 * s.universe().precision())
mp.dps = mp_precision
(tau1, z, tau2) = tuple(s)
(tau1p, zp, tau2p) = (self.level() * tau1, self.level() * z,
self.level() * tau2)
(e_tau1, e_z, e_tau2) = (exp(2 * pi * i * tau1), exp(2 * pi * i * z),
exp(2 * pi * i * tau2))
(e_tau1p, e_zp, e_tau2p) = (exp(2 * pi * i * tau1p),
exp(2 * pi * i * zp),
exp(2 * pi * i * tau2p))
self_value = s.universe().zero()
trans_value = s.universe().zero()
for k in precision:
(a, b, c) = apply_GL_to_form(self._P1List()(k[1]), k[0])
self_value = self_value + self[k] * (e_tau1**a * e_z**b *
e_tau2**c)
trans_value = trans_value + self[k] * (e_tau1p**a * e_zp**b *
e_tau2p**c)
return trans_value / self_value
def __call__(self, g):
"""
Computes the value of a character self on a group element
g (g must be an element of self.group())
EXAMPLES:
sage: F = AbelianGroup(5, [2,3,5,7,8], names="abcde")
sage: a,b,c,d,e = F.gens()
sage: Fd = DualAbelianGroup(F, names="ABCDE")
sage: A,B,C,D,E = Fd.gens()
sage: A*B^2*D^7
A*B^2
sage: A(a) ## random last few digits
-1.0000000000000000 + 0.00000000000000013834419720915037*I
sage: B(b) ## random last few digits
-0.49999999999999983 + 0.86602540378443871*I
sage: A(a*b) ## random last few digits
-1.0000000000000000 + 0.00000000000000013834419720915037*I
"""
F = self.parent().base_ring()
expsX = list(self.list())
expsg = list(g.list())
invs = self.parent().invariants()
N = LCM(invs)
if is_ComplexField(F):
from sage.symbolic.constants import pi
I = F.gen()
PI = F(pi)
ans = prod([
exp(2 * PI * I * expsX[i] * expsg[i] / invs[i])
for i in range(len(expsX))
])
return ans
ans = F(1) ## assumes F is the cyclotomic field
zeta = F.gen()
#print F,zeta
for i in range(len(expsX)):
inv_noti = N / invs[i]
ans = ans * zeta**(expsX[i] * expsg[i] * inv_noti)
return ans
def __call__(self,g):
"""
Computes the value of a character self on a group element
g (g must be an element of self.group())
EXAMPLES:
sage: F = AbelianGroup(5, [2,3,5,7,8], names="abcde")
sage: a,b,c,d,e = F.gens()
sage: Fd = DualAbelianGroup(F, names="ABCDE")
sage: A,B,C,D,E = Fd.gens()
sage: A*B^2*D^7
A*B^2
sage: A(a) ## random last few digits
-1.0000000000000000 + 0.00000000000000013834419720915037*I
sage: B(b) ## random last few digits
-0.49999999999999983 + 0.86602540378443871*I
sage: A(a*b) ## random last few digits
-1.0000000000000000 + 0.00000000000000013834419720915037*I
"""
F = self.parent().base_ring()
expsX = list(self.list())
expsg = list(g.list())
invs = self.parent().invariants()
N = LCM(invs)
if is_ComplexField(F):
from sage.symbolic.constants import pi
I = F.gen()
PI = F(pi)
ans = prod([exp(2*PI*I*expsX[i]*expsg[i]/invs[i]) for i in range(len(expsX))])
return ans
ans = F(1) ## assumes F is the cyclotomic field
zeta = F.gen()
#print F,zeta
for i in range(len(expsX)):
inv_noti = N/invs[i]
ans = ans*zeta**(expsX[i]*expsg[i]*inv_noti)
return ans
def isogenies_prime_degree(self, l=None, max_l=31):
"""
Generic code, valid for all fields, for arbitrary prime `l` not equal to the characteristic.
INPUT:
- ``l`` -- either None, a prime or a list of primes.
- ``max_l`` -- a bound on the primes to be tested (ignored unless `l` is None).
OUTPUT:
(list) All `l`-isogenies for the given `l` with domain self.
METHOD:
Calls the generic function
``isogenies_prime_degree()``. This requires that
certain operations have been implemented over the base field,
such as root-finding for univariate polynomials.
EXAMPLES::
sage: F = QQbar
sage: E = EllipticCurve(F, [1,18]); E
Elliptic Curve defined by y^2 = x^3 + x + 18 over Algebraic Field
sage: E.isogenies_prime_degree()
Traceback (most recent call last):
...
NotImplementedError: This code could be implemented for QQbar, but has not been yet.
sage: F = CC
sage: E = EllipticCurve(F, [1,18]); E
Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 18.0000000000000 over Complex Field with 53 bits of precision
sage: E.isogenies_prime_degree(11)
Traceback (most recent call last):
...
NotImplementedError: This code could be implemented for general complex fields, but has not been yet.
Examples over finite fields::
sage: E = EllipticCurve(GF(next_prime(1000000)), [7,8])
sage: E.isogenies_prime_degree()
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 970389*x + 794257 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 29783*x + 206196 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 999960*x + 78 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 878063*x + 845666 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 375648*x + 342776 over Finite Field of size 1000003, Isogeny of degree 17 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 347438*x + 594729 over Finite Field of size 1000003, Isogeny of degree 17 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 674846*x + 7392 over Finite Field of size 1000003, Isogeny of degree 23 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 390065*x + 605596 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 970389*x + 794257 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 29783*x + 206196 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 999960*x + 78 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree(3)
[]
sage: E.isogenies_prime_degree(5)
[]
sage: E.isogenies_prime_degree(7)
[]
sage: E.isogenies_prime_degree(13)
[Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 878063*x + 845666 over Finite Field of size 1000003,
Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 375648*x + 342776 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree([2, 3, 5, 7, 13])
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 970389*x + 794257 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 29783*x + 206196 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 999960*x + 78 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 878063*x + 845666 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 375648*x + 342776 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree([2, 4])
Traceback (most recent call last):
...
ValueError: 4 is not prime.
sage: E.isogenies_prime_degree(4)
Traceback (most recent call last):
...
ValueError: 4 is not prime.
sage: E.isogenies_prime_degree(11)
[]
sage: E = EllipticCurve(GF(17),[2,0])
sage: E.isogenies_prime_degree(3)
[]
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x over Finite Field of size 17 to Elliptic Curve defined by y^2 = x^3 + 9*x over Finite Field of size 17, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x over Finite Field of size 17 to Elliptic Curve defined by y^2 = x^3 + 5*x + 9 over Finite Field of size 17, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x over Finite Field of size 17 to Elliptic Curve defined by y^2 = x^3 + 5*x + 8 over Finite Field of size 17]
sage: E = EllipticCurve(GF(13^4, 'a'),[2,8])
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + 7*x + 4 over Finite Field in a of size 13^4, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + (8*a^3+2*a^2+7*a+5)*x + (12*a^3+3*a^2+4*a+4) over Finite Field in a of size 13^4, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + (5*a^3+11*a^2+6*a+11)*x + (a^3+10*a^2+9*a) over Finite Field in a of size 13^4]
sage: E.isogenies_prime_degree(3)
[Isogeny of degree 3 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + 9*x + 11 over Finite Field in a of size 13^4]
Example to show that separable isogenies of degree equal to the characteristic are now implemented::
sage: E.isogenies_prime_degree(13)
[Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + 6*x + 5 over Finite Field in a of size 13^4]
Examples over number fields (other than QQ)::
sage: QQroot2.<e> = NumberField(x^2-2)
sage: E = EllipticCurve(QQroot2, j=8000)
sage: E.isogenies_prime_degree()
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + (-150528000)*x + (-629407744000) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 = x^3 + (-602112000)*x + 5035261952000 over Number Field in e with defining polynomial x^2 - 2,
Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + (-150528000)*x + (-629407744000) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 = x^3 + (903168000*e-1053696000)*x + (14161674240000*e-23288086528000) over Number Field in e with defining polynomial x^2 - 2,
Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + (-150528000)*x + (-629407744000) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 = x^3 + (-903168000*e-1053696000)*x + (-14161674240000*e-23288086528000) over Number Field in e with defining polynomial x^2 - 2]
sage: E = EllipticCurve(QQroot2, [1,0,1,4, -6]); E
Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 + x*y + y = x^3 + (-36)*x + (-70) over Number Field in e with defining polynomial x^2 - 2]
sage: E.isogenies_prime_degree(3)
[Isogeny of degree 3 from Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 + x*y + y = x^3 + (-128/3)*x + 5662/27 over Number Field in e with defining polynomial x^2 - 2, Isogeny of degree 3 from Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 + x*y + y = x^3 + (-171)*x + (-874) over Number Field in e with defining polynomial x^2 - 2]
"""
F = self.base_ring()
if is_RealField(F):
raise NotImplementedError("This code could be implemented for general real fields, but has not been yet.")
if is_ComplexField(F):
raise NotImplementedError("This code could be implemented for general complex fields, but has not been yet.")
if F == rings.QQbar:
raise NotImplementedError("This code could be implemented for QQbar, but has not been yet.")
from isogeny_small_degree import isogenies_prime_degree
if l is None:
from sage.rings.all import prime_range
l = prime_range(max_l+1)
if not isinstance(l, list):
try:
l = rings.ZZ(l)
except TypeError:
raise ValueError("%s is not prime."%l)
if l.is_prime():
return isogenies_prime_degree(self, l)
else:
raise ValueError("%s is not prime."%l)
L = list(set(l))
try:
L = [rings.ZZ(l) for l in L]
except TypeError:
raise ValueError("%s is not a list of primes."%l)
L.sort()
return sum([isogenies_prime_degree(self,l) for l in L],[])
def _singular_init_(self, singular=singular):
"""
Return a newly created Singular ring matching this ring.
EXAMPLES::
sage: PolynomialRing(QQ,'u_ba')._singular_init_()
// characteristic : 0
// number of vars : 1
// block 1 : ordering lp
// : names u_ba
// block 2 : ordering C
"""
if not can_convert_to_singular(self):
raise TypeError("no conversion of this ring to a Singular ring defined")
if self.ngens()==1:
_vars = '(%s)'%self.gen()
if "*" in _vars: # 1.000...000*x
_vars = _vars.split("*")[1]
order = 'lp'
else:
_vars = str(self.gens())
order = self.term_order().singular_str()
base_ring = self.base_ring()
if is_RealField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
precision = base_ring.precision()
digits = sage.arith.all.integer_ceil((2*precision - 2)/7.0)
self.__singular = singular.ring("(real,%d,0)"%digits, _vars, order=order, check=False)
elif is_ComplexField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
precision = base_ring.precision()
digits = sage.arith.all.integer_ceil((2*precision - 2)/7.0)
self.__singular = singular.ring("(complex,%d,0,I)"%digits, _vars, order=order, check=False)
elif is_RealDoubleField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
self.__singular = singular.ring("(real,15,0)", _vars, order=order, check=False)
elif is_ComplexDoubleField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
self.__singular = singular.ring("(complex,15,0,I)", _vars, order=order, check=False)
elif base_ring.is_prime_field():
self.__singular = singular.ring(self.characteristic(), _vars, order=order, check=False)
elif sage.rings.finite_rings.finite_field_constructor.is_FiniteField(base_ring):
# not the prime field!
gen = str(base_ring.gen())
r = singular.ring( "(%s,%s)"%(self.characteristic(),gen), _vars, order=order, check=False)
self.__minpoly = (str(base_ring.modulus()).replace("x",gen)).replace(" ","")
if singular.eval('minpoly') != "(" + self.__minpoly + ")":
singular.eval("minpoly=%s"%(self.__minpoly) )
self.__minpoly = singular.eval('minpoly')[1:-1]
self.__singular = r
elif number_field.number_field_base.is_NumberField(base_ring) and base_ring.is_absolute():
# not the rationals!
gen = str(base_ring.gen())
poly=base_ring.polynomial()
poly_gen=str(poly.parent().gen())
poly_str=str(poly).replace(poly_gen,gen)
r = singular.ring( "(%s,%s)"%(self.characteristic(),gen), _vars, order=order, check=False)
self.__minpoly = (poly_str).replace(" ","")
if singular.eval('minpoly') != "(" + self.__minpoly + ")":
singular.eval("minpoly=%s"%(self.__minpoly) )
self.__minpoly = singular.eval('minpoly')[1:-1]
self.__singular = r
elif sage.rings.fraction_field.is_FractionField(base_ring) and (base_ring.base_ring() is ZZ or base_ring.base_ring().is_prime_field() or is_FiniteField(base_ring.base_ring())):
if base_ring.ngens()==1:
gens = str(base_ring.gen())
else:
gens = str(base_ring.gens())
if not (not base_ring.base_ring().is_prime_field() and is_FiniteField(base_ring.base_ring())) :
self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gens), _vars, order=order, check=False)
else:
ext_gen = str(base_ring.base_ring().gen())
_vars = '(' + ext_gen + ', ' + _vars[1:];
R = self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gens), _vars, order=order, check=False)
self.base_ring().__minpoly = (str(base_ring.base_ring().modulus()).replace("x",ext_gen)).replace(" ","")
singular.eval('setring '+R._name);
self.__singular = singular("std(ideal(%s))"%(self.base_ring().__minpoly),type='qring')
elif sage.rings.function_field.function_field.is_RationalFunctionField(base_ring) and base_ring.constant_field().is_prime_field():
gen = str(base_ring.gen())
self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gen), _vars, order=order, check=False)
elif is_IntegerModRing(base_ring):
ch = base_ring.characteristic()
if ch.is_power_of(2):
exp = ch.nbits() -1
self.__singular = singular.ring("(integer,2,%d)"%(exp,), _vars, order=order, check=False)
else:
self.__singular = singular.ring("(integer,%d)"%(ch,), _vars, order=order, check=False)
elif base_ring is ZZ:
self.__singular = singular.ring("(integer)", _vars, order=order, check=False)
else:
raise TypeError("no conversion to a Singular ring defined")
return self.__singular
def _singular_init_(self, singular=singular):
"""
Return a newly created Singular ring matching this ring.
EXAMPLES::
sage: PolynomialRing(QQ,'u_ba')._singular_init_()
polynomial ring, over a field, global ordering
// coefficients: QQ
// number of vars : 1
// block 1 : ordering lp
// : names u_ba
// block 2 : ordering C
"""
if not can_convert_to_singular(self):
raise TypeError("no conversion of this ring to a Singular ring defined")
if self.ngens()==1:
_vars = '(%s)'%self.gen()
if "*" in _vars: # 1.000...000*x
_vars = _vars.split("*")[1]
order = 'lp'
else:
_vars = str(self.gens())
order = self.term_order().singular_str()
base_ring = self.base_ring()
if is_RealField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
precision = base_ring.precision()
digits = sage.arith.all.integer_ceil((2*precision - 2)/7.0)
self.__singular = singular.ring("(real,%d,0)"%digits, _vars, order=order, check=False)
elif is_ComplexField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
precision = base_ring.precision()
digits = sage.arith.all.integer_ceil((2*precision - 2)/7.0)
self.__singular = singular.ring("(complex,%d,0,I)"%digits, _vars, order=order, check=False)
elif is_RealDoubleField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
self.__singular = singular.ring("(real,15,0)", _vars, order=order, check=False)
elif is_ComplexDoubleField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
self.__singular = singular.ring("(complex,15,0,I)", _vars, order=order, check=False)
elif base_ring.is_prime_field():
self.__singular = singular.ring(self.characteristic(), _vars, order=order, check=False)
elif sage.rings.finite_rings.finite_field_constructor.is_FiniteField(base_ring):
# not the prime field!
gen = str(base_ring.gen())
r = singular.ring( "(%s,%s)"%(self.characteristic(),gen), _vars, order=order, check=False)
self.__minpoly = (str(base_ring.modulus()).replace("x",gen)).replace(" ","")
if singular.eval('minpoly') != "(" + self.__minpoly + ")":
singular.eval("minpoly=%s"%(self.__minpoly) )
self.__minpoly = singular.eval('minpoly')[1:-1]
self.__singular = r
elif number_field.number_field_base.is_NumberField(base_ring) and base_ring.is_absolute():
# not the rationals!
gen = str(base_ring.gen())
poly=base_ring.polynomial()
poly_gen=str(poly.parent().gen())
poly_str=str(poly).replace(poly_gen,gen)
r = singular.ring( "(%s,%s)"%(self.characteristic(),gen), _vars, order=order, check=False)
self.__minpoly = (poly_str).replace(" ","")
if singular.eval('minpoly') != "(" + self.__minpoly + ")":
singular.eval("minpoly=%s"%(self.__minpoly) )
self.__minpoly = singular.eval('minpoly')[1:-1]
self.__singular = r
elif sage.rings.fraction_field.is_FractionField(base_ring) and (base_ring.base_ring() is ZZ or base_ring.base_ring().is_prime_field() or is_FiniteField(base_ring.base_ring())):
if base_ring.ngens()==1:
gens = str(base_ring.gen())
else:
gens = str(base_ring.gens())
if not (not base_ring.base_ring().is_prime_field() and is_FiniteField(base_ring.base_ring())) :
self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gens), _vars, order=order, check=False)
else:
ext_gen = str(base_ring.base_ring().gen())
_vars = '(' + ext_gen + ', ' + _vars[1:];
R = self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gens), _vars, order=order, check=False)
self.base_ring().__minpoly = (str(base_ring.base_ring().modulus()).replace("x",ext_gen)).replace(" ","")
singular.eval('setring '+R._name);
from sage.misc.stopgap import stopgap
stopgap("Denominators of fraction field elements are sometimes dropped without warning.", 17696)
self.__singular = singular("std(ideal(%s))"%(self.base_ring().__minpoly),type='qring')
elif sage.rings.function_field.function_field.is_RationalFunctionField(base_ring) and base_ring.constant_field().is_prime_field():
gen = str(base_ring.gen())
self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gen), _vars, order=order, check=False)
elif is_IntegerModRing(base_ring):
ch = base_ring.characteristic()
if ch.is_power_of(2):
exp = ch.nbits() -1
self.__singular = singular.ring("(integer,2,%d)"%(exp,), _vars, order=order, check=False)
else:
self.__singular = singular.ring("(integer,%d)"%(ch,), _vars, order=order, check=False)
elif base_ring is ZZ:
self.__singular = singular.ring("(integer)", _vars, order=order, check=False)
else:
raise TypeError("no conversion to a Singular ring defined")
return self.__singular
def _evalf_(self, n, x, **kwds):
"""
Evaluates :class:`chebyshev_T` numerically with mpmath.
EXAMPLES::
sage: chebyshev_T._evalf_(10,3)
2.26195370000000e7
sage: chebyshev_T._evalf_(10,3,parent=RealField(75))
2.261953700000000000000e7
sage: chebyshev_T._evalf_(10,I)
-3363.00000000000
sage: chebyshev_T._evalf_(5,0.3)
0.998880000000000
sage: chebyshev_T(1/2, 0)
0.707106781186548
sage: chebyshev_T(1/2, 3/2)
1.11803398874989
sage: chebyshev_T._evalf_(1.5, Mod(8,9))
Traceback (most recent call last):
...
TypeError: cannot evaluate chebyshev_T with parent Ring of integers modulo 9
This simply evaluates using :class:`RealField` or :class:`ComplexField`::
sage: chebyshev_T(1234.5, RDF(2.1))
5.48174256255782e735
sage: chebyshev_T(1234.5, I)
-1.21629397684152e472 - 1.21629397684152e472*I
For large values of ``n``, mpmath fails (but the algebraic formula
still works)::
sage: chebyshev_T._evalf_(10^6, 0.1)
Traceback (most recent call last):
...
NoConvergence: Hypergeometric series converges too slowly. Try increasing maxterms.
sage: chebyshev_T(10^6, 0.1)
0.636384327171504
"""
try:
real_parent = kwds['parent']
except KeyError:
real_parent = parent(x)
if not is_RealField(real_parent) and not is_ComplexField(
real_parent):
# parent is not a real or complex field: figure out a good parent
if x in RR:
x = RR(x)
real_parent = RR
elif x in CC:
x = CC(x)
real_parent = CC
if not is_RealField(real_parent) and not is_ComplexField(real_parent):
raise TypeError(
"cannot evaluate chebyshev_T with parent {}".format(
real_parent))
from sage.libs.mpmath.all import call as mpcall
from sage.libs.mpmath.all import chebyt as mpchebyt
return mpcall(mpchebyt, n, x, parent=real_parent)
trans_value = trans_value + self[k] * (e_tau1p**a * e_zp**b * e_tau2p**c)
return trans_value / self_value
def schmidt_t5_eigenvalue_numerical(self, (tau1, z, tau2)) :
from sage.libs.mpmath import mp
from sage.libs.mpmath.mp import exp, pi
from sage.libs.mpmath.mp import j as i
if not Integer(self.__level()).is_prime() :
raise ValueError, "T_5 is only unique if the level is a prime"
precision = ParamodularFormD2Filter_trace(self.precision())
s = Sequence([tau1, z, tau2])
if not is_ComplexField(s) :
mp_precision = 30
else :
mp_precision = ceil(3.33 * s.universe().precision())
mp.dps = mp_precision
p1list = P1List(self.level())
## Prepare the operation for d_1(N)
## We have to invert the lifts since we will later use apply_GL_to_form
d1_matrices = [p1list.lift_to_sl2z(i) for i in xrange(len(p1list))]
d1_matrices = map(lambda (a,b,c,d): (d,-b,-c,a), d1_matrices)
## Prepare the evaluation points corresponding to d_02(N)
d2_points = list()
for i in xrange(len(p1list())) :
def lfun_character(chi):
"""
Create the L-function of a primitive Dirichlet character.
If the given character is not primitive, it is replaced by its
associated primitive character.
OUTPUT:
one :pari:`lfun` object
EXAMPLES::
sage: from sage.lfunctions.pari import lfun_character, LFunction
sage: chi = DirichletGroup(6).gen().primitive_character()
sage: L = LFunction(lfun_character(chi))
sage: L(3)
1.20205690315959
TESTS:
A non-primitive one::
sage: L = LFunction(lfun_character(DirichletGroup(6).gen()))
sage: L(4)
1.08232323371114
With complex arguments::
sage: from sage.lfunctions.pari import lfun_character, LFunction
sage: chi = DirichletGroup(6, CC).gen().primitive_character()
sage: L = LFunction(lfun_character(chi))
sage: L(3)
1.20205690315959
"""
if not chi.is_primitive():
chi = chi.primitive_character()
conductor = chi.conductor()
G = pari.znstar(conductor, 1)
pari_orders = [pari(o) for o in G[2][1]]
pari_gens = IntegerModRing(conductor).unit_gens(algorithm="pari")
# should coincide with G[2][2]
values_on_gens = (chi(x) for x in pari_gens)
# now compute the input for pari (list of exponents)
P = chi.parent()
if is_ComplexField(P.base_ring()):
zeta = P.zeta()
zeta_argument = zeta.argument()
v = [int(x.argument() / zeta_argument) for x in values_on_gens]
else:
dlog = P._zeta_dlog
v = [dlog[x] for x in values_on_gens]
m = P.zeta_order()
v = [(vi * oi) // m for vi, oi in zip(v, pari_orders)]
return pari.lfuncreate([G, v])
def _evalf_(self, n, x, **kwds):
"""
Evaluates :class:`chebyshev_T` numerically with mpmath.
EXAMPLES::
sage: chebyshev_T._evalf_(10,3)
2.26195370000000e7
sage: chebyshev_T._evalf_(10,3,parent=RealField(75))
2.261953700000000000000e7
sage: chebyshev_T._evalf_(10,I)
-3363.00000000000
sage: chebyshev_T._evalf_(5,0.3)
0.998880000000000
sage: chebyshev_T(1/2, 0)
0.707106781186548
sage: chebyshev_T(1/2, 3/2)
1.11803398874989
sage: chebyshev_T._evalf_(1.5, Mod(8,9))
Traceback (most recent call last):
...
TypeError: cannot evaluate chebyshev_T with parent Ring of integers modulo 9
This simply evaluates using :class:`RealField` or :class:`ComplexField`::
sage: chebyshev_T(1234.5, RDF(2.1))
5.48174256255782e735
sage: chebyshev_T(1234.5, I)
-1.21629397684152e472 - 1.21629397684152e472*I
For large values of ``n``, mpmath fails (but the algebraic formula
still works)::
sage: chebyshev_T._evalf_(10^6, 0.1)
Traceback (most recent call last):
...
NoConvergence: Hypergeometric series converges too slowly. Try increasing maxterms.
sage: chebyshev_T(10^6, 0.1)
0.636384327171504
"""
try:
real_parent = kwds["parent"]
except KeyError:
real_parent = parent(x)
if not is_RealField(real_parent) and not is_ComplexField(real_parent):
# parent is not a real or complex field: figure out a good parent
if x in RR:
x = RR(x)
real_parent = RR
elif x in CC:
x = CC(x)
real_parent = CC
if not is_RealField(real_parent) and not is_ComplexField(real_parent):
raise TypeError("cannot evaluate chebyshev_T with parent {}".format(real_parent))
from sage.libs.mpmath.all import call as mpcall
from sage.libs.mpmath.all import chebyt as mpchebyt
return mpcall(mpchebyt, n, x, parent=real_parent)
def isogenies_prime_degree(self, l=None, max_l=31):
"""
Generic code, valid for all fields, for arbitrary prime `l` not equal to the characteristic.
INPUT:
- ``l`` -- either None, a prime or a list of primes.
- ``max_l`` -- a bound on the primes to be tested (ignored unless `l` is None).
OUTPUT:
(list) All `l`-isogenies for the given `l` with domain self.
METHOD:
Calls the generic function
``isogenies_prime_degree()``. This requires that
certain operations have been implemented over the base field,
such as root-finding for univariate polynomials.
EXAMPLES::
sage: F = QQbar
sage: E = EllipticCurve(F, [1,18]); E
Elliptic Curve defined by y^2 = x^3 + x + 18 over Algebraic Field
sage: E.isogenies_prime_degree()
Traceback (most recent call last):
...
NotImplementedError: This code could be implemented for QQbar, but has not been yet.
sage: F = CC
sage: E = EllipticCurve(F, [1,18]); E
Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 18.0000000000000 over Complex Field with 53 bits of precision
sage: E.isogenies_prime_degree(11)
Traceback (most recent call last):
...
NotImplementedError: This code could be implemented for general complex fields, but has not been yet.
Examples over finite fields::
sage: E = EllipticCurve(GF(next_prime(1000000)), [7,8])
sage: E.isogenies_prime_degree()
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 970389*x + 794257 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 29783*x + 206196 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 999960*x + 78 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 878063*x + 845666 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 375648*x + 342776 over Finite Field of size 1000003, Isogeny of degree 17 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 347438*x + 594729 over Finite Field of size 1000003, Isogeny of degree 17 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 674846*x + 7392 over Finite Field of size 1000003, Isogeny of degree 23 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 390065*x + 605596 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 970389*x + 794257 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 29783*x + 206196 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 999960*x + 78 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree(3)
[]
sage: E.isogenies_prime_degree(5)
[]
sage: E.isogenies_prime_degree(7)
[]
sage: E.isogenies_prime_degree(13)
[Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 878063*x + 845666 over Finite Field of size 1000003,
Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 375648*x + 342776 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree([2, 3, 5, 7, 13])
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 970389*x + 794257 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 29783*x + 206196 over Finite Field of size 1000003, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 999960*x + 78 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 878063*x + 845666 over Finite Field of size 1000003, Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 7*x + 8 over Finite Field of size 1000003 to Elliptic Curve defined by y^2 = x^3 + 375648*x + 342776 over Finite Field of size 1000003]
sage: E.isogenies_prime_degree([2, 4])
Traceback (most recent call last):
...
ValueError: 4 is not prime.
sage: E.isogenies_prime_degree(4)
Traceback (most recent call last):
...
ValueError: 4 is not prime.
sage: E.isogenies_prime_degree(11)
[]
sage: E = EllipticCurve(GF(17),[2,0])
sage: E.isogenies_prime_degree(3)
[]
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x over Finite Field of size 17 to Elliptic Curve defined by y^2 = x^3 + 9*x over Finite Field of size 17, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x over Finite Field of size 17 to Elliptic Curve defined by y^2 = x^3 + 5*x + 9 over Finite Field of size 17, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x over Finite Field of size 17 to Elliptic Curve defined by y^2 = x^3 + 5*x + 8 over Finite Field of size 17]
sage: E = EllipticCurve(GF(13^4, 'a'),[2,8])
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + 7*x + 4 over Finite Field in a of size 13^4, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + (8*a^3+2*a^2+7*a+5)*x + (12*a^3+3*a^2+4*a+4) over Finite Field in a of size 13^4, Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + (5*a^3+11*a^2+6*a+11)*x + (a^3+10*a^2+9*a) over Finite Field in a of size 13^4]
sage: E.isogenies_prime_degree(3)
[Isogeny of degree 3 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + 9*x + 11 over Finite Field in a of size 13^4]
Example to show that separable isogenies of degree equal to the characteristic are now implemented::
sage: E.isogenies_prime_degree(13)
[Isogeny of degree 13 from Elliptic Curve defined by y^2 = x^3 + 2*x + 8 over Finite Field in a of size 13^4 to Elliptic Curve defined by y^2 = x^3 + 6*x + 5 over Finite Field in a of size 13^4]
Examples over number fields (other than QQ)::
sage: QQroot2.<e> = NumberField(x^2-2)
sage: E = EllipticCurve(QQroot2, j=8000)
sage: E.isogenies_prime_degree()
[Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + (-150528000)*x + (-629407744000) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 = x^3 + (-36750)*x + 2401000 over Number Field in e with defining polynomial x^2 - 2,
Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + (-150528000)*x + (-629407744000) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 = x^3 + (220500*e-257250)*x + (54022500*e-88837000) over Number Field in e with defining polynomial x^2 - 2,
Isogeny of degree 2 from Elliptic Curve defined by y^2 = x^3 + (-150528000)*x + (-629407744000) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 = x^3 + (-220500*e-257250)*x + (-54022500*e-88837000) over Number Field in e with defining polynomial x^2 - 2]
sage: E = EllipticCurve(QQroot2, [1,0,1,4, -6]); E
Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2
sage: E.isogenies_prime_degree(2)
[Isogeny of degree 2 from Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 + x*y + y = x^3 + (-36)*x + (-70) over Number Field in e with defining polynomial x^2 - 2]
sage: E.isogenies_prime_degree(3)
[Isogeny of degree 3 from Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 + x*y + y = x^3 + (-1)*x over Number Field in e with defining polynomial x^2 - 2,
Isogeny of degree 3 from Elliptic Curve defined by y^2 + x*y + y = x^3 + 4*x + (-6) over Number Field in e with defining polynomial x^2 - 2 to Elliptic Curve defined by y^2 + x*y + y = x^3 + (-171)*x + (-874) over Number Field in e with defining polynomial x^2 - 2]
"""
F = self.base_ring()
if is_RealField(F):
raise NotImplementedError(
"This code could be implemented for general real fields, but has not been yet."
)
if is_ComplexField(F):
raise NotImplementedError(
"This code could be implemented for general complex fields, but has not been yet."
)
if F == rings.QQbar:
raise NotImplementedError(
"This code could be implemented for QQbar, but has not been yet."
)
from isogeny_small_degree import isogenies_prime_degree
if l is None:
from sage.rings.all import prime_range
l = prime_range(max_l + 1)
if not isinstance(l, list):
try:
l = rings.ZZ(l)
except TypeError:
raise ValueError("%s is not prime." % l)
if l.is_prime():
return isogenies_prime_degree(self, l)
else:
raise ValueError("%s is not prime." % l)
L = list(set(l))
try:
L = [rings.ZZ(l) for l in L]
except TypeError:
raise ValueError("%s is not a list of primes." % l)
L.sort()
return sum([isogenies_prime_degree(self, l) for l in L], [])
def has_rational_point(self, point = False,
algorithm = 'default', read_cache = True):
r"""
Returns True if and only if the conic ``self``
has a point over its base field `B`.
If ``point`` is True, then returns a second output, which is
a rational point if one exists.
Points are cached whenever they are found. Cached information
is used if and only if ``read_cache`` is True.
ALGORITHM:
The parameter ``algorithm`` specifies the algorithm
to be used:
- ``'default'`` -- If the base field is real or complex,
use an elementary native Sage implementation.
- ``'magma'`` (requires Magma to be installed) --
delegates the task to the Magma computer algebra
system.
EXAMPLES:
sage: Conic(RR, [1, 1, 1]).has_rational_point()
False
sage: Conic(CC, [1, 1, 1]).has_rational_point()
True
sage: Conic(RR, [1, 2, -3]).has_rational_point(point = True)
(True, (1.73205080756888 : 0.000000000000000 : 1.00000000000000))
Conics over polynomial rings can not be solved yet without Magma::
sage: R.<t> = QQ[]
sage: C = Conic([-2,t^2+1,t^2-1])
sage: C.has_rational_point()
Traceback (most recent call last):
...
NotImplementedError: has_rational_point not implemented for conics over base field Fraction Field of Univariate Polynomial Ring in t over Rational Field
But they can be solved with Magma::
sage: C.has_rational_point(algorithm='magma') # optional - magma
True
sage: C.has_rational_point(algorithm='magma', point=True) # optional - magma
(True, (t : 1 : 1))
sage: D = Conic([t,1,t^2])
sage: D.has_rational_point(algorithm='magma') # optional - magma
False
TESTS:
One of the following fields comes with an embedding into the complex
numbers, one does not. Check that they are both handled correctly by
the Magma interface. ::
sage: K.<i> = QuadraticField(-1)
sage: K.coerce_embedding()
Generic morphism:
From: Number Field in i with defining polynomial x^2 + 1
To: Complex Lazy Field
Defn: i -> 1*I
sage: Conic(K, [1,1,1]).rational_point(algorithm='magma') # optional - magma
(-i : 1 : 0)
sage: x = QQ['x'].gen()
sage: L.<i> = NumberField(x^2+1, embedding=None)
sage: Conic(L, [1,1,1]).rational_point(algorithm='magma') # optional - magma
(-i : 1 : 0)
sage: L == K
False
"""
if read_cache:
if self._rational_point is not None:
if point:
return True, self._rational_point
else:
return True
B = self.base_ring()
if algorithm == 'magma':
from sage.interfaces.magma import magma
M = magma(self)
b = M.HasRationalPoint().sage()
if not point:
return b
if not b:
return False, None
M_pt = M.HasRationalPoint(nvals=2)[1]
# Various attempts will be made to convert `pt` to
# a Sage object. The end result will always be checked
# by self.point().
pt = [M_pt[1], M_pt[2], M_pt[3]]
# The first attempt is to use sequences. This is efficient and
# succeeds in cases where the Magma interface fails to convert
# number field elements, because embeddings between number fields
# may be lost on conversion to and from Magma.
# This should deal with all absolute number fields.
try:
return True, self.point([B(c.Eltseq().sage()) for c in pt])
except TypeError:
pass
# The second attempt tries to split Magma elements into
# numerators and denominators first. This is neccessary
# for the field of rational functions, because (at the moment of
# writing) fraction field elements are not converted automatically
# from Magma to Sage.
try:
return True, self.point( \
[B(c.Numerator().sage()/c.Denominator().sage()) for c in pt])
except (TypeError, NameError):
pass
# Finally, let the Magma interface handle conversion.
try:
return True, self.point([B(c.sage()) for c in pt])
except (TypeError, NameError):
pass
raise NotImplementedError("No correct conversion implemented for converting the Magma point %s on %s to a correct Sage point on self (=%s)" % (M_pt, M, self))
if algorithm != 'default':
raise ValueError("Unknown algorithm: %s" % algorithm)
if is_ComplexField(B):
if point:
[_,_,_,d,e,f] = self._coefficients
if d == 0:
return True, self.point([0,1,0])
return True, self.point([0, ((e**2-4*d*f).sqrt()-e)/(2*d), 1],
check = False)
return True
if is_RealField(B):
D, T = self.diagonal_matrix()
[a, b, c] = [D[0,0], D[1,1], D[2,2]]
if a == 0:
ret = True, self.point(T*vector([1,0,0]), check = False)
elif a*c <= 0:
ret = True, self.point(T*vector([(-c/a).sqrt(),0,1]),
check = False)
elif b == 0:
ret = True, self.point(T*vector([0,1,0]), check = False)
elif b*c <= 0:
ret = True, self.point(T*vector([0,(-c/b).sqrt(),0,1]),
check = False)
else:
ret = False, None
if point:
return ret
return ret[0]
raise NotImplementedError("has_rational_point not implemented for " \
"conics over base field %s" % B)
def elliptic_j(z, prec=53):
r"""
Returns the elliptic modular `j`-function evaluated at `z`.
INPUT:
- ``z`` (complex) -- a complex number with positive imaginary part.
- ``prec`` (default: 53) -- precision in bits for the complex field.
OUTPUT:
(complex) The value of `j(z)`.
ALGORITHM:
Calls the ``pari`` function ``ellj()``.
AUTHOR:
John Cremona
EXAMPLES::
sage: elliptic_j(CC(i))
1728.00000000000
sage: elliptic_j(sqrt(-2.0))
8000.00000000000
sage: z = ComplexField(100)(1,sqrt(11))/2
sage: elliptic_j(z)
-32768.000...
sage: elliptic_j(z).real().round()
-32768
::
sage: tau = (1 + sqrt(-163))/2
sage: (-elliptic_j(tau.n(100)).real().round())^(1/3)
640320
This example shows the need for higher precision than the default one of
the `ComplexField`, see :trac:`28355`::
sage: -elliptic_j(tau) # rel tol 1e-2
2.62537412640767e17 - 732.558854258998*I
sage: -elliptic_j(tau,75) # rel tol 1e-2
2.625374126407680000000e17 - 0.0001309913593909879441262*I
sage: -elliptic_j(tau,100) # rel tol 1e-2
2.6253741264076799999999999999e17 - 1.3012822400356887122945119790e-12*I
sage: (-elliptic_j(tau, 100).real().round())^(1/3)
640320
"""
CC = z.parent()
from sage.rings.complex_field import is_ComplexField
if not is_ComplexField(CC):
CC = ComplexField(prec)
try:
z = CC(z)
except ValueError:
raise ValueError("elliptic_j only defined for complex arguments.")
from sage.libs.all import pari
return CC(pari(z).ellj())
def _singular_init_(self, singular=singular_default):
"""
Return a newly created Singular ring matching this ring.
EXAMPLES::
sage: PolynomialRing(QQ,'u_ba')._singular_init_()
// characteristic : 0
// number of vars : 1
// block 1 : ordering lp
// : names u_ba
// block 2 : ordering C
"""
if not can_convert_to_singular(self):
raise TypeError, "no conversion of this ring to a Singular ring defined"
if self.ngens()==1:
_vars = '(%s)'%self.gen()
if "*" in _vars: # 1.000...000*x
_vars = _vars.split("*")[1]
order = 'lp'
else:
_vars = str(self.gens())
order = self.term_order().singular_str()
base_ring = self.base_ring()
if is_RealField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
precision = base_ring.precision()
digits = sage.rings.arith.integer_ceil((2*precision - 2)/7.0)
self.__singular = singular.ring("(real,%d,0)"%digits, _vars, order=order, check=False)
elif is_ComplexField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
precision = base_ring.precision()
digits = sage.rings.arith.integer_ceil((2*precision - 2)/7.0)
self.__singular = singular.ring("(complex,%d,0,I)"%digits, _vars, order=order, check=False)
elif is_RealDoubleField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
self.__singular = singular.ring("(real,15,0)", _vars, order=order, check=False)
elif is_ComplexDoubleField(base_ring):
# singular converts to bits from base_10 in mpr_complex.cc by:
# size_t bits = 1 + (size_t) ((float)digits * 3.5);
self.__singular = singular.ring("(complex,15,0,I)", _vars, order=order, check=False)
elif base_ring.is_prime_field():
self.__singular = singular.ring(self.characteristic(), _vars, order=order, check=False)
elif sage.rings.finite_rings.constructor.is_FiniteField(base_ring):
# not the prime field!
gen = str(base_ring.gen())
r = singular.ring( "(%s,%s)"%(self.characteristic(),gen), _vars, order=order, check=False)
self.__minpoly = (str(base_ring.modulus()).replace("x",gen)).replace(" ","")
if singular.eval('minpoly') != "(" + self.__minpoly + ")":
singular.eval("minpoly=%s"%(self.__minpoly) )
self.__minpoly = singular.eval('minpoly')[1:-1]
self.__singular = r
elif number_field.all.is_NumberField(base_ring) and base_ring.is_absolute():
# not the rationals!
gen = str(base_ring.gen())
poly=base_ring.polynomial()
poly_gen=str(poly.parent().gen())
poly_str=str(poly).replace(poly_gen,gen)
r = singular.ring( "(%s,%s)"%(self.characteristic(),gen), _vars, order=order, check=False)
self.__minpoly = (poly_str).replace(" ","")
if singular.eval('minpoly') != "(" + self.__minpoly + ")":
singular.eval("minpoly=%s"%(self.__minpoly) )
self.__minpoly = singular.eval('minpoly')[1:-1]
self.__singular = r
elif sage.rings.fraction_field.is_FractionField(base_ring) and (base_ring.base_ring() is ZZ or base_ring.base_ring().is_prime_field()):
if base_ring.ngens()==1:
gens = str(base_ring.gen())
else:
gens = str(base_ring.gens())
self.__singular = singular.ring( "(%s,%s)"%(base_ring.characteristic(),gens), _vars, order=order, check=False)
elif is_IntegerModRing(base_ring):
ch = base_ring.characteristic()
if ch.is_power_of(2):
exp = ch.nbits() -1
self.__singular = singular.ring("(integer,2,%d)"%(exp,), _vars, order=order, check=False)
else:
self.__singular = singular.ring("(integer,%d)"%(ch,), _vars, order=order, check=False)
elif base_ring is ZZ:
self.__singular = singular.ring("(integer)", _vars, order=order, check=False)
else:
raise TypeError, "no conversion to a Singular ring defined"
return self.__singular
def qrp(A, rank = None, extra_prec = 16):
m = A.nrows()
n = A.ncols()
s = min(m,n)
if rank is not None:
#s = min(s, rank + 1);
pass;
base_prec = A.base_ring().precision();
base_field = A.base_ring()
if is_ComplexField(base_field):
field = ComplexField(base_prec + extra_prec + m);
else:
field = RealField(base_prec + extra_prec + m);
# field = base_field;
R = copy(A);
A = A.change_ring(field);
P = [ j for j in xrange(n) ];
Q = identity_matrix(field,m)
# print A.base_ring()
# print Q.base_ring()
normbound = field(2)**(-0.5*field.precision());
colnorms2 = [ float_sum([ R[k,j].norm() for k in range(m)]) for j in range(n) ];
for j in xrange(s):
# find column with max norm
maxnorm2 = colnorms2[j];
p = j;
for k in xrange(j, n):
if colnorms2[k] > maxnorm2:
p = k;
maxnorm2 = colnorms2[k];
#it is worth it to recompute the maxnorm
xnorm2 = float_sum([ R[i,p].norm() for i in range(j, m)])
xnorm = sqrt(xnorm2);
# swap j and p in A, P and colnorms
if j != p:
P[j], P[p] = P[p], P[j]
colnorms2[j], colnorms2[p] = colnorms2[p], colnorms2[j]
for i in xrange(0, m):
R[i, j], R[i, p] = R[i, p], R[i, j];
# compute householder vector
u = [ R[k,j] for k in xrange(j, m) ];
alpha = R[j,j];
# alphanorm = alpha.abs();
if alpha.real() < 0:
u[0] -= xnorm
z = -1
else:
u[0] += xnorm
z = 1
beta = xnorm*(xnorm + alpha * z);
if beta.abs() < normbound:
beta = float_sum( [u[i].conjugate() * R[i+j,j] for i in range(m - j)])
if beta == field(0):
break;
beta = 1/beta;
# H = I - beta * u * u^*
# Apply householder matrix
#update R
R[j,j] = -z * xnorm;
for i in xrange(j+1,m):
R[i,j] = 0
for k in xrange(j+1, n):
lambdR = beta * float_sum( [u[l - j].conjugate() * R[l, k] for l in xrange(j, m)] );
for i in xrange(j, m):
R[i, k] -= lambdR * u[i - j];
#update Q
for k in xrange(m):
lambdQ = float_sum( [u[l - j].conjugate() * Q[l, k] for l in xrange(j, m)] );
lambdQ *= beta
for i in xrange(j,m):
Q[i, k] -= lambdQ * u[i - j];
for k in xrange(j + 1, n):
square = R[j,k].norm();
colnorms2[k] -= square;
# sometimes is better to just recompute the norm
if True: #colnorms2[k] < normbound or colnorms2[k] < square*normbound:
colnorms2[k] = float_sum([ R[i,k].norm() for i in range(j + 1, m)])
# compute P matrix
Pmatrix = Matrix(ZZ, n);
for i in xrange(n):
Pmatrix[ P[i], i] = 1;
return Q.conjugate_transpose().change_ring(base_field), R.change_ring(base_field), Pmatrix;
