The base class EllipticCurvePoint_field, derived from
AdditiveGroupElement, provides support for points on elliptic
curves defined over general fields. The derived classes
EllipticCurvePoint_number_field and
EllipticCurvePoint_finite_field provide further support for point
on curves defined over number fields (including the rational field
) and over finite fields.
The class EllipticCurvePoint, which is based on SchemeMorphism_point_projective_ring, currently has little extra functionality.
EXAMPLES:
An example over :
sage: E = EllipticCurve('389a1')
sage: P = E(-1,1); P
(-1 : 1 : 1)
sage: Q = E(0,-1); Q
(0 : -1 : 1)
sage: P+Q
(4 : 8 : 1)
sage: P-Q
(1 : 0 : 1)
sage: 3*P-5*Q
(328/361 : -2800/6859 : 1)
An example over a number field:
sage: K.<i> = QuadraticField(-1)
sage: E = EllipticCurve(K,[1,0,0,0,-1])
sage: P = E(0,i); P
(0 : i : 1)
sage: P.order()
+Infinity
sage: 101*P-100*P==P
True
An example over a finite field:
sage: K.<a> = GF(101^3)
sage: E = EllipticCurve(K,[1,0,0,0,-1])
sage: P = E(40*a^2 + 69*a + 84 , 58*a^2 + 73*a + 45)
sage: P.order()
1032210
sage: E.cardinality()
1032210
Arithmetic with a point over an extension of a finite field:
sage: k.<a> = GF(5^2)
sage: E = EllipticCurve(k,[1,0]); E
Elliptic Curve defined by y^2 = x^3 + x over Finite Field in a of size 5^2
sage: P = E([a,2*a+4])
sage: 5*P
(2*a + 3 : 2*a : 1)
sage: P*5
(2*a + 3 : 2*a : 1)
sage: P + P + P + P + P
(2*a + 3 : 2*a : 1)
sage: F = Zmod(3)
sage: E = EllipticCurve(F,[1,0]);
sage: P = E([2,1])
sage: import sys
sage: n = sys.maxsize
sage: P*(n+1)-P*n == P
True
Arithmetic over with composite
is supported. When an
operation tries to invert a non-invertible element, a
ZeroDivisionError is raised and a factorization of the modulus appears
in the error message:
sage: N = 1715761513
sage: E = EllipticCurve(Integers(N),[3,-13])
sage: P = E(2,1)
sage: LCM([2..60])*P
Traceback (most recent call last):
...
ZeroDivisionError: Inverse of 1520944668 does not exist (characteristic = 1715761513 = 26927*63719)
AUTHORS:
Bases: sage.schemes.projective.projective_point.SchemeMorphism_point_projective_ring
A point on an elliptic curve.
Bases: sage.schemes.projective.projective_point.SchemeMorphism_point_abelian_variety_field
A point on an elliptic curve over a field. The point has coordinates in the base field.
EXAMPLES:
sage: E = EllipticCurve('37a')
sage: E([0,0])
(0 : 0 : 1)
sage: E(0,0) # brackets are optional
(0 : 0 : 1)
sage: E([GF(5)(0), 0]) # entries are coerced
(0 : 0 : 1)
sage: E(0.000, 0)
(0 : 0 : 1)
sage: E(1,0,0)
Traceback (most recent call last):
...
TypeError: Coordinates [1, 0, 0] do not define a point on
Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
sage: E = EllipticCurve([0,0,1,-1,0])
sage: S = E(QQ); S
Abelian group of points on Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
sage: K.<i>=NumberField(x^2+1)
sage: E=EllipticCurve(K,[0,1,0,-160,308])
sage: P=E(26,-120)
sage: Q=E(2+12*i,-36+48*i)
sage: P.order() == Q.order() == 4 # long time (3s)
True
sage: 2*P==2*Q
False
sage: K.<t>=FractionField(PolynomialRing(QQ,'t'))
sage: E=EllipticCurve([0,0,0,0,t^2])
sage: P=E(0,t)
sage: P,2*P,3*P
((0 : t : 1), (0 : -t : 1), (0 : 1 : 0))
TESTS:
sage: loads(S.dumps()) == S
True
sage: E = EllipticCurve('37a')
sage: P = E(0,0); P
(0 : 0 : 1)
sage: loads(P.dumps()) == P
True
sage: T = 100*P
sage: loads(T.dumps()) == T
True
Test pickling an elliptic curve that has known points on it:
sage: e = EllipticCurve([0, 0, 1, -1, 0]); g = e.gens(); loads(dumps(e)) == e
True
Test that the refactoring from trac ticket #14711 did preserve the behaviour of domain and codomain:
sage: E=EllipticCurve(QQ,[1,1])
sage: P=E(0,1)
sage: P.domain()
Spectrum of Rational Field
sage: K.<a>=NumberField(x^2-3,'a')
sage: P=E.base_extend(K)(1,a)
sage: P.domain()
Spectrum of Number Field in a with defining polynomial x^2 - 3
sage: P.codomain()
Elliptic Curve defined by y^2 = x^3 + x + 1 over Number Field in a with defining polynomial x^2 - 3
sage: P.codomain() == P.curve()
True
Return the order of this point on the elliptic curve.
If the point is zero, returns 1, otherwise raise a NotImplementedError.
For curves over number fields and finite fields, see below.
Note
additive_order() is a synonym for order()
EXAMPLE:
sage: K.<t>=FractionField(PolynomialRing(QQ,'t'))
sage: E=EllipticCurve([0,0,0,-t^2,0])
sage: P=E(t,0)
sage: P.order()
Traceback (most recent call last):
...
NotImplementedError: Computation of order of a point not implemented over general fields.
sage: E(0).additive_order()
1
sage: E(0).order() == 1
True
Return ate pairing of -torsion points
and
.
Also known as the -th modified ate pairing.
is
-rational,
and
must be an element of
, where
is the
-frobenius map (and hence
is
-rational).
INPUT:
OUTPUT:
FiniteFieldElement in – the ate pairing of
and
.
EXAMPLES:
An example with embedding degree 6:
sage: p = 7549; A = 0; B = 1; n = 157; k = 6; t = 14
sage: F = GF(p); E = EllipticCurve(F, [A, B])
sage: R.<x> = F[]; K.<a> = GF(p^k, modulus=x^k+2)
sage: EK = E.base_extend(K)
sage: P = EK(3050, 5371); Q = EK(6908*a^4, 3231*a^3)
sage: P.ate_pairing(Q, n, k, t)
6708*a^5 + 4230*a^4 + 4350*a^3 + 2064*a^2 + 4022*a + 6733
sage: s = Integer(randrange(1, n))
sage: (s*P).ate_pairing(Q, n, k, t) == P.ate_pairing(s*Q, n, k, t)
True
sage: P.ate_pairing(s*Q, n, k, t) == P.ate_pairing(Q, n, k, t)^s
True
Another example with embedding degree 7 and positive trace:
sage: p = 2213; A = 1; B = 49; n = 1093; k = 7; t = 28
sage: F = GF(p); E = EllipticCurve(F, [A, B])
sage: R.<x> = F[]; K.<a> = GF(p^k, modulus=x^k+2)
sage: EK = E.base_extend(K)
sage: P = EK(1583, 1734)
sage: Qx = 1729*a^6+1767*a^5+245*a^4+980*a^3+1592*a^2+1883*a+722
sage: Qy = 1299*a^6+1877*a^5+1030*a^4+1513*a^3+1457*a^2+309*a+1636
sage: Q = EK(Qx, Qy)
sage: P.ate_pairing(Q, n, k, t)
1665*a^6 + 1538*a^5 + 1979*a^4 + 239*a^3 + 2134*a^2 + 2151*a + 654
sage: s = Integer(randrange(1, n))
sage: (s*P).ate_pairing(Q, n, k, t) == P.ate_pairing(s*Q, n, k, t)
True
sage: P.ate_pairing(s*Q, n, k, t) == P.ate_pairing(Q, n, k, t)^s
True
Another example with embedding degree 7 and negative trace:
sage: p = 2017; A = 1; B = 30; n = 29; k = 7; t = -70
sage: F = GF(p); E = EllipticCurve(F, [A, B])
sage: R.<x> = F[]; K.<a> = GF(p^k, modulus=x^k+2)
sage: EK = E.base_extend(K)
sage: P = EK(369, 716)
sage: Qx = 1226*a^6+1778*a^5+660*a^4+1791*a^3+1750*a^2+867*a+770
sage: Qy = 1764*a^6+198*a^5+1206*a^4+406*a^3+1200*a^2+273*a+1712
sage: Q = EK(Qx, Qy)
sage: P.ate_pairing(Q, n, k, t)
1794*a^6 + 1161*a^5 + 576*a^4 + 488*a^3 + 1950*a^2 + 1905*a + 1315
sage: s = Integer(randrange(1, n))
sage: (s*P).ate_pairing(Q, n, k, t) == P.ate_pairing(s*Q, n, k, t)
True
sage: P.ate_pairing(s*Q, n, k, t) == P.ate_pairing(Q, n, k, t)^s
True
Using the same data, we show that the ate pairing is a power of the Tate pairing (see [HSV] end of section 3.1):
sage: c = (k*p^(k-1)).mod(n); T = t - 1
sage: N = gcd(T^k - 1, p^k - 1)
sage: s = Integer(N/n)
sage: L = Integer((T^k - 1)/N)
sage: M = (L*s*c.inverse_mod(n)).mod(n)
sage: P.ate_pairing(Q, n, k, t) == Q.tate_pairing(P, n, k)^M
True
An example where we have to pass the base field size (and we again have
agreement with the Tate pairing). Note that though is not
-rational, (it is the homomorphic image of an
-rational point) it
is nonetheless in
, and so is a legitimate input:
sage: q = 2^5; F.<a>=GF(q)
sage: n = 41; k = 4; t = -8
sage: E=EllipticCurve(F,[0,0,1,1,1])
sage: P = E(a^4 + 1, a^3)
sage: Fx.<b>=GF(q^k)
sage: Ex=EllipticCurve(Fx,[0,0,1,1,1])
sage: phi=Hom(F,Fx)(F.gen().minpoly().roots(Fx)[0][0])
sage: Px=Ex(phi(P.xy()[0]),phi(P.xy()[1]))
sage: Qx = Ex(b^19+b^18+b^16+b^12+b^10+b^9+b^8+b^5+b^3+1, b^18+b^13+b^10+b^8+b^5+b^4+b^3+b)
sage: Qx = Ex(Qx[0]^q, Qx[1]^q) - Qx # ensure Qx is in ker(pi - q)
sage: Px.ate_pairing(Qx, n, k, t)
Traceback (most recent call last):
...
ValueError: Unexpected field degree: set keyword argument q equal to the size of the base field (big field is GF(q^4)).
sage: Px.ate_pairing(Qx, n, k, t, q)
b^19 + b^18 + b^17 + b^16 + b^15 + b^14 + b^13 + b^12 + b^11 + b^9 + b^8 + b^5 + b^4 + b^2 + b + 1
sage: s = Integer(randrange(1, n))
sage: (s*Px).ate_pairing(Qx, n, k, t, q) == Px.ate_pairing(s*Qx, n, k, t, q)
True
sage: Px.ate_pairing(s*Qx, n, k, t, q) == Px.ate_pairing(Qx, n, k, t, q)^s
True
sage: c = (k*q^(k-1)).mod(n); T = t - 1
sage: N = gcd(T^k - 1, q^k - 1)
sage: s = Integer(N/n)
sage: L = Integer((T^k - 1)/N)
sage: M = (L*s*c.inverse_mod(n)).mod(n)
sage: Px.ate_pairing(Qx, n, k, t, q) == Qx.tate_pairing(Px, n, k, q)^M
True
It is an error if is not in the kernel of
, where
is
the Frobenius automorphism:
sage: p = 29; A = 1; B = 0; n = 5; k = 2; t = 10
sage: F = GF(p); R.<x> = F[]
sage: E = EllipticCurve(F, [A, B]);
sage: K.<a> = GF(p^k, modulus=x^k+2); EK = E.base_extend(K)
sage: P = EK(13, 8); Q = EK(13, 21)
sage: P.ate_pairing(Q, n, k, t)
Traceback (most recent call last):
...
ValueError: Point (13 : 21 : 1) not in Ker(pi - q)
It is also an error if is not in the kernel os
:
sage: p = 29; A = 1; B = 0; n = 5; k = 2; t = 10
sage: F = GF(p); R.<x> = F[]
sage: E = EllipticCurve(F, [A, B]);
sage: K.<a> = GF(p^k, modulus=x^k+2); EK = E.base_extend(K)
sage: P = EK(14, 10*a); Q = EK(13, 21)
sage: P.ate_pairing(Q, n, k, t)
Traceback (most recent call last):
...
ValueError: This point (14 : 10*a : 1) is not in Ker(pi - 1)
NOTES:
First defined in the paper of [HSV], the ate pairing can be computationally effective in those cases when the trace of the curve over the base field is significantly smaller than the expected value. This implementation is simply Miller’s algorithm followed by a naive exponentiation, and makes no claims towards efficiency.
REFERENCES:
[HSV] | (1, 2) Hess, Smart, Vercauteren, “The Eta Pairing Revisited”, IEEE Trans. Information Theory, 52(10): 4595-4602, 2006. |
AUTHORS:
Return the curve that this point is on.
EXAMPLES:
sage: E = EllipticCurve('389a')
sage: P = E([-1,1])
sage: P.curve()
Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field
Return a list of all points such that
where
= self.
Only points on the elliptic curve containing self and defined over the base field are included.
INPUT:
OUTPUT:
(list) – a (possibly empty) list of solutions to
,
where
= self.
EXAMPLES:
We find the five 5-torsion points on an elliptic curve:
sage: E = EllipticCurve('11a'); E
Elliptic Curve defined by y^2 + y = x^3 - x^2 - 10*x - 20 over Rational Field
sage: P = E(0); P
(0 : 1 : 0)
sage: P.division_points(5)
[(0 : 1 : 0), (5 : -6 : 1), (5 : 5 : 1), (16 : -61 : 1), (16 : 60 : 1)]
Note above that 0 is included since [5]*0 = 0.
We create a curve of rank 1 with no torsion and do a consistency check:
sage: E = EllipticCurve('11a').quadratic_twist(-7)
sage: Q = E([44,-270])
sage: (4*Q).division_points(4)
[(44 : -270 : 1)]
We create a curve over a non-prime finite field with group of
order :
sage: k.<a> = GF(25)
sage: E = EllipticCurve(k, [1,2+a,3,4*a,2])
sage: P = E([3,3*a+4])
sage: factor(E.order())
2 * 3^2
sage: P.order()
9
We find the -division points as a consistency check – there
is just one, of course:
sage: P.division_points(1)
[(3 : 3*a + 4 : 1)]
The point has order coprime to 2 but divisible by 3, so:
sage: P.division_points(2)
[(2*a + 1 : 3*a + 4 : 1), (3*a + 1 : a : 1)]
We check that each of the 2-division points works as claimed:
sage: [2*Q for Q in P.division_points(2)]
[(3 : 3*a + 4 : 1), (3 : 3*a + 4 : 1)]
Some other checks:
sage: P.division_points(3)
[]
sage: P.division_points(4)
[(0 : 3*a + 2 : 1), (1 : 0 : 1)]
sage: P.division_points(5)
[(1 : 1 : 1)]
An example over a number field (see trac ticket #3383):
sage: E = EllipticCurve('19a1')
sage: K.<t> = NumberField(x^9-3*x^8-4*x^7+16*x^6-3*x^5-21*x^4+5*x^3+7*x^2-7*x+1)
sage: EK = E.base_extend(K)
sage: E(0).division_points(3)
[(0 : 1 : 0), (5 : -10 : 1), (5 : 9 : 1)]
sage: EK(0).division_points(3)
[(0 : 1 : 0), (5 : 9 : 1), (5 : -10 : 1)]
sage: E(0).division_points(9)
[(0 : 1 : 0), (5 : -10 : 1), (5 : 9 : 1)]
sage: EK(0).division_points(9)
[(0 : 1 : 0), (5 : 9 : 1), (5 : -10 : 1), (-150/121*t^8 + 414/121*t^7 + 1481/242*t^6 - 2382/121*t^5 - 103/242*t^4 + 629/22*t^3 - 367/242*t^2 - 1307/121*t + 625/121 : 35/484*t^8 - 133/242*t^7 + 445/242*t^6 - 799/242*t^5 + 373/484*t^4 + 113/22*t^3 - 2355/484*t^2 - 753/242*t + 1165/484 : 1), (-150/121*t^8 + 414/121*t^7 + 1481/242*t^6 - 2382/121*t^5 - 103/242*t^4 + 629/22*t^3 - 367/242*t^2 - 1307/121*t + 625/121 : -35/484*t^8 + 133/242*t^7 - 445/242*t^6 + 799/242*t^5 - 373/484*t^4 - 113/22*t^3 + 2355/484*t^2 + 753/242*t - 1649/484 : 1), (-1383/484*t^8 + 970/121*t^7 + 3159/242*t^6 - 5211/121*t^5 + 37/484*t^4 + 654/11*t^3 - 909/484*t^2 - 4831/242*t + 6791/484 : 927/121*t^8 - 5209/242*t^7 - 8187/242*t^6 + 27975/242*t^5 - 1147/242*t^4 - 1729/11*t^3 + 1566/121*t^2 + 12873/242*t - 10871/242 : 1), (-1383/484*t^8 + 970/121*t^7 + 3159/242*t^6 - 5211/121*t^5 + 37/484*t^4 + 654/11*t^3 - 909/484*t^2 - 4831/242*t + 6791/484 : -927/121*t^8 + 5209/242*t^7 + 8187/242*t^6 - 27975/242*t^5 + 1147/242*t^4 + 1729/11*t^3 - 1566/121*t^2 - 12873/242*t + 10629/242 : 1), (-4793/484*t^8 + 6791/242*t^7 + 10727/242*t^6 - 18301/121*t^5 + 2347/484*t^4 + 2293/11*t^3 - 7311/484*t^2 - 17239/242*t + 26767/484 : 30847/484*t^8 - 21789/121*t^7 - 34605/121*t^6 + 117164/121*t^5 - 10633/484*t^4 - 29437/22*t^3 + 39725/484*t^2 + 55428/121*t - 176909/484 : 1), (-4793/484*t^8 + 6791/242*t^7 + 10727/242*t^6 - 18301/121*t^5 + 2347/484*t^4 + 2293/11*t^3 - 7311/484*t^2 - 17239/242*t + 26767/484 : -30847/484*t^8 + 21789/121*t^7 + 34605/121*t^6 - 117164/121*t^5 + 10633/484*t^4 + 29437/22*t^3 - 39725/484*t^2 - 55428/121*t + 176425/484 : 1)]
Return True if this point has finite additive order as an element of the group of points on this curve.
For fields other than number fields and finite fields, this is NotImplemented unless self.is_zero().
EXAMPLES:
sage: K.<t>=FractionField(PolynomialRing(QQ,'t'))
sage: E=EllipticCurve([0,0,0,-t^2,0])
sage: P = E(0)
sage: P.has_finite_order()
True
sage: P=E(t,0)
sage: P.has_finite_order()
Traceback (most recent call last):
...
NotImplementedError: Computation of order of a point not implemented over general fields.
sage: (2*P).is_zero()
True
Return True if this point has infinite additive order as an element of the group of points on this curve.
For fields other than number fields and finite fields, this is NotImplemented unless self.is_zero().
EXAMPLES:
sage: K.<t>=FractionField(PolynomialRing(QQ,'t'))
sage: E=EllipticCurve([0,0,0,-t^2,0])
sage: P = E(0)
sage: P.has_infinite_order()
False
sage: P=E(t,0)
sage: P.has_infinite_order()
Traceback (most recent call last):
...
NotImplementedError: Computation of order of a point not implemented over general fields.
sage: (2*P).is_zero()
True
Return True if there exists a point defined over the same
field as self such that
== self.
INPUT:
OUTPUT:
(bool) – True if there is a solution, else False.
Warning
This function usually triggers the computation of the
-th division polynomial of the associated elliptic
curve, which will be expensive if
is large, though it
will be cached for subsequent calls with the same
.
EXAMPLES:
sage: E = EllipticCurve('389a')
sage: Q = 5*E(0,0); Q
(-2739/1444 : -77033/54872 : 1)
sage: Q.is_divisible_by(4)
False
sage: Q.is_divisible_by(5)
True
A finite field example:
sage: E = EllipticCurve(GF(101),[23,34])
sage: E.cardinality().factor()
2 * 53
sage: Set([T.order() for T in E.points()])
{1, 106, 2, 53}
sage: len([T for T in E.points() if T.is_divisible_by(2)])
53
sage: len([T for T in E.points() if T.is_divisible_by(3)])
106
TESTS:
This shows that the bug reported at trac ticket #10076 is fixed:
sage: K = QuadraticField(8,'a')
sage: E = EllipticCurve([K(0),0,0,-1,0])
sage: P = E([-1,0])
sage: P.is_divisible_by(2)
False
sage: P.division_points(2)
[]
Note that it is not sufficient to test that self.division_points(m,poly_only=True) has roots:
sage: P.division_points(2, poly_only=True).roots()
[(1/2*a - 1, 1), (-1/2*a - 1, 1)]
sage: tor = E.torsion_points(); len(tor)
8
sage: [T.order() for T in tor]
[2, 4, 4, 2, 1, 2, 4, 4]
sage: all([T.is_divisible_by(3) for T in tor])
True
sage: Set([T for T in tor if T.is_divisible_by(2)])
{(0 : 1 : 0), (1 : 0 : 1)}
sage: Set([2*T for T in tor])
{(0 : 1 : 0), (1 : 0 : 1)}
Return True if this point has finite additive order as an element of the group of points on this curve.
For fields other than number fields and finite fields, this is NotImplemented unless self.is_zero().
EXAMPLES:
sage: K.<t>=FractionField(PolynomialRing(QQ,'t'))
sage: E=EllipticCurve([0,0,0,-t^2,0])
sage: P = E(0)
sage: P.has_finite_order()
True
sage: P=E(t,0)
sage: P.has_finite_order()
Traceback (most recent call last):
...
NotImplementedError: Computation of order of a point not implemented over general fields.
sage: (2*P).is_zero()
True
Return the order of this point on the elliptic curve.
If the point is zero, returns 1, otherwise raise a NotImplementedError.
For curves over number fields and finite fields, see below.
Note
additive_order() is a synonym for order()
EXAMPLE:
sage: K.<t>=FractionField(PolynomialRing(QQ,'t'))
sage: E=EllipticCurve([0,0,0,-t^2,0])
sage: P=E(t,0)
sage: P.order()
Traceback (most recent call last):
...
NotImplementedError: Computation of order of a point not implemented over general fields.
sage: E(0).additive_order()
1
sage: E(0).order() == 1
True
Plot this point on an elliptic curve.
INPUT:
EXAMPLES:
sage: E = EllipticCurve('389a')
sage: P = E([-1,1])
sage: P.plot(pointsize=30, rgbcolor=(1,0,0))
Graphics object consisting of 1 graphics primitive
Return the scheme of this point, i.e., the curve it is on. This is synonymous with curve() which is perhaps more intuitive.
EXAMPLES:
sage: E=EllipticCurve(QQ,[1,1])
sage: P=E(0,1)
sage: P.scheme()
Elliptic Curve defined by y^2 = x^3 + x + 1 over Rational Field
sage: P.scheme() == P.curve()
True
sage: K.<a>=NumberField(x^2-3,'a')
sage: P=E.base_extend(K)(1,a)
sage: P.scheme()
Elliptic Curve defined by y^2 = x^3 + x + 1 over Number Field in a with defining polynomial x^2 - 3
Set the value of self._order to value.
Use this when you know a priori the order of this point to avoid a potentially expensive order calculation.
INPUT:
OUTPUT:
None
EXAMPLES:
This example illustrates basic usage.
sage: E = EllipticCurve(GF(7), [0, 1]) # This curve has order 6
sage: G = E(5, 0)
sage: G.set_order(2)
sage: 2*G
(0 : 1 : 0)
We now give a more interesting case, the NIST-P521 curve. Its order is too big to calculate with SAGE, and takes a long time using other packages, so it is very useful here.
sage: p = 2^521 - 1
sage: prev_proof_state = proof.arithmetic()
sage: proof.arithmetic(False) # turn off primality checking
sage: F = GF(p)
sage: A = p - 3
sage: B = 1093849038073734274511112390766805569936207598951683748994586394495953116150735016013708737573759623248592132296706313309438452531591012912142327488478985984
sage: q = 6864797660130609714981900799081393217269435300143305409394463459185543183397655394245057746333217197532963996371363321113864768612440380340372808892707005449
sage: E = EllipticCurve([F(A), F(B)])
sage: G = E.random_point()
sage: G.set_order(q)
sage: G.order() * G # This takes practically no time.
(0 : 1 : 0)
sage: proof.arithmetic(prev_proof_state) # restore state
It is an error to pass a equal to
:
sage: E = EllipticCurve(GF(7), [0, 1]) # This curve has order 6
sage: G = E.random_point()
sage: G.set_order(0)
Traceback (most recent call last):
...
ValueError: Value 0 illegal for point order
sage: G.set_order(1000)
Traceback (most recent call last):
...
ValueError: Value 1000 illegal: outside max Hasse bound
It is also very likely an error to pass a value which is not the actual order of this point. How unlikely is determined by the factorization of the actual order, and the actual group structure:
sage: E = EllipticCurve(GF(7), [0, 1]) # This curve has order 6
sage: G = E(5, 0) # G has order 2
sage: G.set_order(11)
Traceback (most recent call last):
...
ValueError: Value 11 illegal: 11 * (5 : 0 : 1) is not the identity
However, set_order can be fooled, though it’s not likely in “real cases of interest”. For instance, the order can be set to a multiple the actual order:
sage: E = EllipticCurve(GF(7), [0, 1]) # This curve has order 6
sage: G = E(5, 0) # G has order 2
sage: G.set_order(8)
sage: G.order()
8
NOTES:
The implementation is based of the fact that orders of elliptic curve points are cached in the (pseudo-private) _order slot.
AUTHORS:
- Mariah Lenox (2011-02-16)
Return Tate pairing of -torsion point
and point
.
The value returned is where
is a function with
divisor
. This is also known as the “modified Tate
pairing”. It is a well-defined bilinear map.
INPUT:
OUTPUT:
An ‘th root of unity in the base field self.curve().base_field()
EXAMPLES:
A simple example, pairing a point with itself, and pairing a point with another rational point:
sage: p = 103; A = 1; B = 18; E = EllipticCurve(GF(p), [A, B])
sage: P = E(33, 91); n = P.order(); n
19
sage: k = GF(n)(p).multiplicative_order(); k
6
sage: P.tate_pairing(P, n, k)
1
sage: Q = E(87, 51)
sage: P.tate_pairing(Q, n, k)
1
sage: set_random_seed(35)
sage: P.tate_pairing(P,n,k)
1
We now let Q be a point on the same curve as above, but defined over the pairing extension field, and we also demonstrate the bilinearity of the pairing:
sage: K.<a> = GF(p^k)
sage: EK = E.base_extend(K); P = EK(P)
sage: Qx = 69*a^5 + 96*a^4 + 22*a^3 + 86*a^2 + 6*a + 35
sage: Qy = 34*a^5 + 24*a^4 + 16*a^3 + 41*a^2 + 4*a + 40
sage: Q = EK(Qx, Qy);
sage: # multiply by cofactor so Q has order n:
sage: h = 551269674; Q = h*Q
sage: P = EK(P); P.tate_pairing(Q, n, k)
24*a^5 + 34*a^4 + 3*a^3 + 69*a^2 + 86*a + 45
sage: s = Integer(randrange(1,n))
sage: ans1 = (s*P).tate_pairing(Q, n, k)
sage: ans2 = P.tate_pairing(s*Q, n, k)
sage: ans3 = P.tate_pairing(Q, n, k)^s
sage: ans1 == ans2 == ans3
True
sage: (ans1 != 1) and (ans1^n == 1)
True
Here is an example of using the Tate pairing to compute the Weil pairing (using the same data as above):
sage: e = Integer((p^k-1)/n); e
62844857712
sage: P.weil_pairing(Q, n)^e
94*a^5 + 99*a^4 + 29*a^3 + 45*a^2 + 57*a + 34
sage: P.tate_pairing(Q, n, k) == P._miller_(Q, n)^e
True
sage: Q.tate_pairing(P, n, k) == Q._miller_(P, n)^e
True
sage: P.tate_pairing(Q, n, k)/Q.tate_pairing(P, n, k)
94*a^5 + 99*a^4 + 29*a^3 + 45*a^2 + 57*a + 34
An example where we have to pass the base field size (and we again have agreement with the Weil pairing):
sage: F.<a>=GF(2^5)
sage: E=EllipticCurve(F,[0,0,1,1,1])
sage: P = E(a^4 + 1, a^3)
sage: Fx.<b>=GF(2^(4*5))
sage: Ex=EllipticCurve(Fx,[0,0,1,1,1])
sage: phi=Hom(F,Fx)(F.gen().minpoly().roots(Fx)[0][0])
sage: Px=Ex(phi(P.xy()[0]),phi(P.xy()[1]))
sage: Qx = Ex(b^19+b^18+b^16+b^12+b^10+b^9+b^8+b^5+b^3+1, b^18+b^13+b^10+b^8+b^5+b^4+b^3+b)
sage: Px.tate_pairing(Qx, n=41, k=4)
Traceback (most recent call last):
...
ValueError: Unexpected field degree: set keyword argument q equal to the size of the base field (big field is GF(q^4)).
sage: num = Px.tate_pairing(Qx, n=41, k=4, q=32); num
b^19 + b^14 + b^13 + b^12 + b^6 + b^4 + b^3
sage: den = Qx.tate_pairing(Px, n=41, k=4, q=32); den
b^19 + b^17 + b^16 + b^15 + b^14 + b^10 + b^6 + b^2 + 1
sage: e = Integer((32^4-1)/41); e
25575
sage: Px.weil_pairing(Qx, 41)^e == num/den
True
NOTES:
This function uses Miller’s algorithm, followed by a naive
exponentiation. It does not do anything fancy. In the case
that there is an issue with being on one of the lines
generated in the
calculation,
is offset by a random
point
and P.tate_pairing(Q+R,n,k)/P.tate_pairing(R,n,k)
is returned.
AUTHORS:
Compute the Weil pairing of self and using Miller’s algorithm.
INPUT:
OUTPUT:
An ‘th root of unity in the base field self.curve().base_field()
EXAMPLES:
sage: F.<a>=GF(2^5)
sage: E=EllipticCurve(F,[0,0,1,1,1])
sage: P = E(a^4 + 1, a^3)
sage: Fx.<b>=GF(2^(4*5))
sage: Ex=EllipticCurve(Fx,[0,0,1,1,1])
sage: phi=Hom(F,Fx)(F.gen().minpoly().roots(Fx)[0][0])
sage: Px=Ex(phi(P.xy()[0]),phi(P.xy()[1]))
sage: O = Ex(0)
sage: Qx = Ex(b^19 + b^18 + b^16 + b^12 + b^10 + b^9 + b^8 + b^5 + b^3 + 1, b^18 + b^13 + b^10 + b^8 + b^5 + b^4 + b^3 + b)
sage: Px.weil_pairing(Qx,41) == b^19 + b^15 + b^9 + b^8 + b^6 + b^4 + b^3 + b^2 + 1
True
sage: Px.weil_pairing(17*Px,41) == Fx(1)
True
sage: Px.weil_pairing(O,41) == Fx(1)
True
An error is raised if either point is not n-torsion:
sage: Px.weil_pairing(O,40)
Traceback (most recent call last):
...
ValueError: points must both be n-torsion
A larger example (see trac ticket #4964):
sage: P,Q = EllipticCurve(GF(19^4,'a'),[-1,0]).gens()
sage: P.order(), Q.order()
(360, 360)
sage: z = P.weil_pairing(Q,360)
sage: z.multiplicative_order()
360
An example over a number field:
sage: P,Q = EllipticCurve('11a1').change_ring(CyclotomicField(5)).torsion_subgroup().gens() # long time (10s)
sage: P,Q = (P.element(), Q.element()) # long time
sage: (P.order(),Q.order()) # long time
(5, 5)
sage: P.weil_pairing(Q,5) # long time
zeta5^2
sage: Q.weil_pairing(P,5) # long time
zeta5^3
ALGORITHM:
Implemented using Proposition 8 in [Mil04]. The value 1 is
returned for linearly dependent input points. This condition
is caught via a DivisionByZeroError, since the use of a
discrete logarithm test for linear dependence, is much too slow
for large .
REFERENCES:
[Mil04] | Victor S. Miller, “The Weil pairing, and its efficient calculation”, J. Cryptol., 17(4):235-261, 2004 |
AUTHOR:
Return the and
coordinates of this point, as a 2-tuple.
If this is the point at infinity a ZeroDivisionError is raised.
EXAMPLES:
sage: E = EllipticCurve('389a')
sage: P = E([-1,1])
sage: P.xy()
(-1, 1)
sage: Q = E(0); Q
(0 : 1 : 0)
sage: Q.xy()
Traceback (most recent call last):
...
ZeroDivisionError: Rational division by zero
Bases: sage.schemes.elliptic_curves.ell_point.EllipticCurvePoint_field
Class for elliptic curve points over finite fields.
Return the order of this point on the elliptic curve.
ALGORITHM:
Use generic functions from sage.groups.generic. If the group order is known, use order_from_multiple(), otherwise use order_from_bounds() with the Hasse bounds for the base field. In the latter case, we might find that we have a generator for the group, in which case it is cached.
We do not cause the group order to be calculated when not
known, since this function is used in determining the group
order via computation of several random points and their
orders. The exceptions to this are (1) when the base field is
a prime field and efficient SEA-based methods are available
for the cardinality, and (2) when finding the group order is
possible quickly, currently only implemented for curves with
or
(see trac ticket #15567).
Note
additive_order() is a synonym for order()
AUTHOR:
EXAMPLES:
sage: k.<a> = GF(5^5)
sage: E = EllipticCurve(k,[2,4]); E
Elliptic Curve defined by y^2 = x^3 + 2*x + 4 over Finite Field in a of size 5^5
sage: P = E(3*a^4 + 3*a , 2*a + 1 )
sage: P.order()
3227
sage: Q = E(0,2)
sage: Q.order()
7
sage: Q.additive_order()
7
In the next example, the cardinality of E will be computed (using SEA) and cached:
sage: p=next_prime(2^150)
sage: E=EllipticCurve(GF(p),[1,1])
sage: P=E(831623307675610677632782670796608848711856078, 42295786042873366706573292533588638217232964)
sage: P.order()
1427247692705959881058262545272474300628281448
sage: P.order()==E.cardinality()
True
In the next example, the cardinality of E will be computed and
cached since :
sage: p = 33554501
sage: F.<u> = GF(p^2)
sage: E = EllipticCurve(F,[0,1])
sage: E.j_invariant()
0
sage: P = E.random_point()
sage: P = E.random_point()
sage: P.order() # random
16777251
sage: E._order # as cached
1125904604468004
Similarly when :
sage: p = 33554473
sage: F.<u> = GF(p^2)
sage: E = EllipticCurve(F,[1,0])
sage: E.j_invariant()
1728
sage: P = E.random_point()
sage: P.order() # random
46912611635760
sage: E._order # as cached
1125902679258240
Returns discrete log of with respect to
=self.
INPUT:
OUTPUT:
(integer) – The discrete log of with respect to
, which is an
integer
with
such that
, if one
exists. A ValueError is raised if there is no solution.
Note
The order of self is computed if not supplied.
AUTHOR:
EXAMPLE:
sage: F = GF(3^6,'a')
sage: a = F.gen()
sage: E = EllipticCurve([0,1,1,a,a])
sage: E.cardinality()
762
sage: A = E.abelian_group()
sage: P = A.gen(0).element()
sage: Q = 400*P
sage: P.discrete_log(Q)
400
Return the order of this point on the elliptic curve.
ALGORITHM:
Use generic functions from sage.groups.generic. If the group order is known, use order_from_multiple(), otherwise use order_from_bounds() with the Hasse bounds for the base field. In the latter case, we might find that we have a generator for the group, in which case it is cached.
We do not cause the group order to be calculated when not
known, since this function is used in determining the group
order via computation of several random points and their
orders. The exceptions to this are (1) when the base field is
a prime field and efficient SEA-based methods are available
for the cardinality, and (2) when finding the group order is
possible quickly, currently only implemented for curves with
or
(see trac ticket #15567).
Note
additive_order() is a synonym for order()
AUTHOR:
EXAMPLES:
sage: k.<a> = GF(5^5)
sage: E = EllipticCurve(k,[2,4]); E
Elliptic Curve defined by y^2 = x^3 + 2*x + 4 over Finite Field in a of size 5^5
sage: P = E(3*a^4 + 3*a , 2*a + 1 )
sage: P.order()
3227
sage: Q = E(0,2)
sage: Q.order()
7
sage: Q.additive_order()
7
In the next example, the cardinality of E will be computed (using SEA) and cached:
sage: p=next_prime(2^150)
sage: E=EllipticCurve(GF(p),[1,1])
sage: P=E(831623307675610677632782670796608848711856078, 42295786042873366706573292533588638217232964)
sage: P.order()
1427247692705959881058262545272474300628281448
sage: P.order()==E.cardinality()
True
In the next example, the cardinality of E will be computed and
cached since :
sage: p = 33554501
sage: F.<u> = GF(p^2)
sage: E = EllipticCurve(F,[0,1])
sage: E.j_invariant()
0
sage: P = E.random_point()
sage: P = E.random_point()
sage: P.order() # random
16777251
sage: E._order # as cached
1125904604468004
Similarly when :
sage: p = 33554473
sage: F.<u> = GF(p^2)
sage: E = EllipticCurve(F,[1,0])
sage: E.j_invariant()
1728
sage: P = E.random_point()
sage: P.order() # random
46912611635760
sage: E._order # as cached
1125902679258240
Bases: sage.schemes.elliptic_curves.ell_point.EllipticCurvePoint_field
A point on an elliptic curve over a number field.
Most of the functionality is derived from the parent class EllipticCurvePoint_field. In addition we have support for orders, heights, reduction modulo primes, and elliptic logarithms.
EXAMPLES:
sage: E = EllipticCurve('37a')
sage: E([0,0])
(0 : 0 : 1)
sage: E(0,0) # brackets are optional
(0 : 0 : 1)
sage: E([GF(5)(0), 0]) # entries are coerced
(0 : 0 : 1)
sage: E(0.000, 0)
(0 : 0 : 1)
sage: E(1,0,0)
Traceback (most recent call last):
...
TypeError: Coordinates [1, 0, 0] do not define a point on
Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
sage: E = EllipticCurve([0,0,1,-1,0])
sage: S = E(QQ); S
Abelian group of points on Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
TESTS:
sage: loads(S.dumps()) == S
True
sage: P = E(0,0); P
(0 : 0 : 1)
sage: loads(P.dumps()) == P
True
sage: T = 100*P
sage: loads(T.dumps()) == T
True
Test pickling an elliptic curve that has known points on it:
sage: e = EllipticCurve([0, 0, 1, -1, 0]); g = e.gens(); loads(dumps(e)) == e
True
Return the order of this point on the elliptic curve.
If the point has infinite order, returns +Infinity. For
curves defined over , we call PARI; over other
number fields we implement the function here.
Note
additive_order() is a synonym for order()
EXAMPLES:
sage: E = EllipticCurve([0,0,1,-1,0])
sage: P = E([0,0]); P
(0 : 0 : 1)
sage: P.order()
+Infinity
sage: E = EllipticCurve([0,1])
sage: P = E([-1,0])
sage: P.order()
2
sage: P.additive_order()
2
Compute the local height of self at the archimedean place .
INPUT:
OUTPUT:
A real number. The normalisation is twice that in Silverman’s paper [Sil1988]. Note that this local height depends on the model of the curve.
ALGORITHM:
See [Sil1988], Section 4.
EXAMPLES:
Examples 1, 2, and 3 from [Sil1988]:
sage: K.<a> = QuadraticField(-2)
sage: E = EllipticCurve(K, [0,-1,1,0,0]); E
Elliptic Curve defined by y^2 + y = x^3 + (-1)*x^2 over Number Field in a with defining polynomial x^2 + 2
sage: P = E.lift_x(2+a); P
(a + 2 : 2*a + 1 : 1)
sage: P.archimedean_local_height(K.places(prec=170)[0]) / 2
0.45754773287523276736211210741423654346576029814695
sage: K.<i> = NumberField(x^2+1)
sage: E = EllipticCurve(K, [0,0,4,6*i,0]); E
Elliptic Curve defined by y^2 + 4*y = x^3 + 6*i*x over Number Field in i with defining polynomial x^2 + 1
sage: P = E((0,0))
sage: P.archimedean_local_height(K.places()[0]) / 2
0.510184995162373
sage: Q = E.lift_x(-9/4); Q
(-9/4 : -27/8*i : 1)
sage: Q.archimedean_local_height(K.places()[0]) / 2
0.654445619529600
An example over the rational numbers:
sage: E = EllipticCurve([0, 0, 0, -36, 0])
sage: P = E([-3, 9])
sage: P.archimedean_local_height()
1.98723816350773
Local heights of torsion points can be non-zero (unlike the global height):
sage: K.<i> = QuadraticField(-1)
sage: E = EllipticCurve([0, 0, 0, K(1), 0])
sage: P = E(i, 0)
sage: P.archimedean_local_height()
0.346573590279973
TESTS:
See trac ticket #12509:
sage: x = polygen(QQ)
sage: K.<a> = NumberField(x^2-x-1)
sage: v = [0, a + 1, 1, 28665*a - 46382, 2797026*a - 4525688]
sage: E = EllipticCurve(v)
sage: P = E([72*a - 509/5, -682/25*a - 434/25])
sage: P.archimedean_local_height()
-0.2206607955468278492183362746930
Deprecated: Use archimedean_local_height() instead. See trac ticket #13951 for details.
Returns the elliptic logarithm of this elliptic curve point.
An embedding of the base field into or
(with
arbitrary precision) may be given; otherwise the first real
embedding is used (with the specified precision) if any, else
the first complex embedding.
INPUT:
ALGORITHM:
See [Co2] Cohen H., A Course in Computational Algebraic Number Theory GTM 138, Springer 1996 for the case of real embeddings, and Cremona, J.E. and Thongjunthug , T. 2010 for the complex case.
AUTHORS:
EXAMPLES:
sage: E = EllipticCurve('389a')
sage: E.discriminant() > 0
True
sage: P = E([-1,1])
sage: P.is_on_identity_component ()
False
sage: P.elliptic_logarithm (precision=96)
0.4793482501902193161295330101 + 0.985868850775824102211203849...*I
sage: Q=E([3,5])
sage: Q.is_on_identity_component()
True
sage: Q.elliptic_logarithm (precision=96)
1.931128271542559442488585220
An example with negative discriminant, and a torsion point:
sage: E = EllipticCurve('11a1')
sage: E.discriminant() < 0
True
sage: P = E([16,-61])
sage: P.elliptic_logarithm(precision=70)
0.25384186085591068434
sage: E.period_lattice().real_period(prec=70) / P.elliptic_logarithm(precision=70)
5.0000000000000000000
A larger example. The default algorithm uses PARI and makes sure the result has the requested precision:
sage: E = EllipticCurve([1, 0, 1, -85357462, 303528987048]) #18074g1
sage: P = E([4458713781401/835903744, -64466909836503771/24167649046528, 1])
sage: P.elliptic_logarithm() # 100 bits
0.27656204014107061464076203097
The native algorithm ‘sage’ used to have trouble with precision in this example, but no longer:
sage: P.elliptic_logarithm(algorithm='sage') # 100 bits
0.27656204014107061464076203097
This shows that the bug reported at trac ticket #4901 has been fixed:
sage: E = EllipticCurve("4390c2")
sage: P = E(683762969925/44944,-565388972095220019/9528128)
sage: P.elliptic_logarithm()
0.00025638725886520225353198932529
sage: P.elliptic_logarithm(precision=64)
0.000256387258865202254
sage: P.elliptic_logarithm(precision=65)
0.0002563872588652022535
sage: P.elliptic_logarithm(precision=128)
0.00025638725886520225353198932528666427412
sage: P.elliptic_logarithm(precision=129)
0.00025638725886520225353198932528666427412
sage: P.elliptic_logarithm(precision=256)
0.0002563872588652022535319893252866642741168388008346370015005142128009610936373
sage: P.elliptic_logarithm(precision=257)
0.00025638725886520225353198932528666427411683880083463700150051421280096109363730
Examples over number fields:
sage: K.<a> = NumberField(x^3-2)
sage: embs = K.embeddings(CC)
sage: E = EllipticCurve([0,1,0,a,a])
sage: Ls = [E.period_lattice(e) for e in embs]
sage: [L.real_flag for L in Ls]
[0, 0, -1]
sage: P = E(-1,0) # order 2
sage: [L.elliptic_logarithm(P) for L in Ls]
[-1.73964256006716 - 1.07861534489191*I, -0.363756518406398 - 1.50699412135253*I, 1.90726488608927]
sage: E = EllipticCurve([-a^2 - a - 1, a^2 + a])
sage: Ls = [E.period_lattice(e) for e in embs]
sage: pts = [E(2*a^2 - a - 1 , -2*a^2 - 2*a + 6 ), E(-2/3*a^2 - 1/3 , -4/3*a - 2/3 ), E(5/4*a^2 - 1/2*a , -a^2 - 1/4*a + 9/4 ), E(2*a^2 + 3*a + 4 , -7*a^2 - 10*a - 12 )]
sage: [[L.elliptic_logarithm(P) for P in pts] for L in Ls]
[[0.250819591818930 - 0.411963479992219*I, -0.290994550611374 - 1.37239400324105*I, -0.693473752205595 - 2.45028458830342*I, -0.151659609775291 - 1.48985406505459*I], [1.33444787667954 - 1.50889756650544*I, 0.792633734249234 - 0.548467043256610*I, 0.390154532655013 + 0.529423541805758*I, 0.931968675085317 - 0.431006981443071*I], [1.14758249500109 + 0.853389664016075*I, 2.59823462472518 + 0.853389664016075*I, 1.75372176444709, 0.303069634723001]]
sage: K.<i> = QuadraticField(-1)
sage: E = EllipticCurve([0,0,0,9*i-10,21-i])
sage: emb = K.embeddings(CC)[1]
sage: L = E.period_lattice(emb)
sage: P = E(2-i,4+2*i)
sage: L.elliptic_logarithm(P,prec=100)
0.70448375537782208460499649302 - 0.79246725643650979858266018068*I
Return True iff this point has finite order on the elliptic curve.
EXAMPLES:
sage: E = EllipticCurve([0,0,1,-1,0])
sage: P = E([0,0]); P
(0 : 0 : 1)
sage: P.has_finite_order()
False
sage: E = EllipticCurve([0,1])
sage: P = E([-1,0])
sage: P.has_finite_order()
True
Returns True iff this point has good reduction modulo a prime.
INPUT:
OUTPUT:
(bool) If a prime of the base field is specified, returns
True iff the point has good reduction at
; otherwise,
return true if the point has god reduction at all primes in
the support of the discriminant of this model.
EXAMPLES:
sage: E = EllipticCurve('990e1')
sage: P = E.gen(0); P
(15 : 51 : 1)
sage: [E.has_good_reduction(p) for p in [2,3,5,7]]
[False, False, False, True]
sage: [P.has_good_reduction(p) for p in [2,3,5,7]]
[True, False, True, True]
sage: [E.tamagawa_exponent(p) for p in [2,3,5,7]]
[2, 2, 1, 1]
sage: [(2*P).has_good_reduction(p) for p in [2,3,5,7]]
[True, True, True, True]
sage: P.has_good_reduction()
False
sage: (2*P).has_good_reduction()
True
sage: (3*P).has_good_reduction()
False
sage: K.<i> = NumberField(x^2+1)
sage: E = EllipticCurve(K,[0,1,0,-160,308])
sage: P = E(26,-120)
sage: E.discriminant().support()
[Fractional ideal (i + 1),
Fractional ideal (-i - 2),
Fractional ideal (2*i + 1),
Fractional ideal (3)]
sage: [E.tamagawa_exponent(p) for p in E.discriminant().support()]
[1, 4, 4, 4]
sage: P.has_good_reduction()
False
sage: (2*P).has_good_reduction()
False
sage: (4*P).has_good_reduction()
True
TESTS:
An example showing that trac ticket #8498 is fixed:
sage: E = EllipticCurve('11a1')
sage: K.<t> = NumberField(x^2+47)
sage: EK = E.base_extend(K)
sage: T = EK(5,5)
sage: P = EK(-2, -1/2*t - 1/2)
sage: p = K.ideal(11)
sage: T.has_good_reduction(p)
False
sage: P.has_good_reduction(p)
True
Return True iff this point has infinite order on the elliptic curve.
EXAMPLES:
sage: E = EllipticCurve([0,0,1,-1,0])
sage: P = E([0,0]); P
(0 : 0 : 1)
sage: P.has_infinite_order()
True
sage: E = EllipticCurve([0,1])
sage: P = E([-1,0])
sage: P.has_infinite_order()
False
Return the Néron-Tate canonical height of the point.
INPUT:
OUTPUT:
The rational number 0, or a non-negative real number.
There are two normalisations used in the literature, one of which is double the other. We use the larger of the two, which is the one appropriate for the BSD conjecture. This is consistent with [Cre] and double that of [SilBook].
See Wikipedia article Néron-Tate height
REFERENCES:
[Cre] | John Cremona, Algorithms for Modular Elliptic Curves. Cambridge University Press, 1997. |
[Sil1988] | (1, 2, 3, 4, 5, 6) Joseph H. Silverman, Computing heights on elliptic curves. Mathematics of Computation, Vol. 51, No. 183 (Jul., 1988), pp. 339-358. |
[SilBook] | Joseph H. Silverman, The Arithmetic of Elliptic Curves. Second edition. Graduate Texts in Mathematics, 106. Springer, 2009. |
EXAMPLES:
sage: E = EllipticCurve('11a'); E
Elliptic Curve defined by y^2 + y = x^3 - x^2 - 10*x - 20 over Rational Field
sage: P = E([5,5]); P
(5 : 5 : 1)
sage: P.height()
0
sage: Q = 5*P
sage: Q.height()
0
sage: E = EllipticCurve('37a'); E
Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
sage: P = E([0,0])
sage: P.height()
0.0511114082399688
sage: P.order()
+Infinity
sage: E.regulator()
0.0511114082399688...
sage: def naive_height(P):
... return log(RR(max(abs(P[0].numerator()), abs(P[0].denominator()))))
sage: for n in [1..10]:
... print naive_height(2^n*P)/4^n
0.000000000000000
0.0433216987849966
0.0502949347635656
0.0511006335618645
0.0511007834799612
0.0511013666152466
0.0511034199907743
0.0511106492906471
0.0511114081541082
0.0511114081541180
sage: E = EllipticCurve('4602a1'); E
Elliptic Curve defined by y^2 + x*y = x^3 + x^2 - 37746035*x - 89296920339 over Rational Field
sage: x = 77985922458974949246858229195945103471590
sage: y = 19575260230015313702261379022151675961965157108920263594545223
sage: d = 2254020761884782243
sage: E([ x / d^2, y / d^3 ]).height()
86.7406561381275
sage: E = EllipticCurve([17, -60, -120, 0, 0]); E
Elliptic Curve defined by y^2 + 17*x*y - 120*y = x^3 - 60*x^2 over Rational Field
sage: E([30, -90]).height()
0
sage: E = EllipticCurve('389a1'); E
Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field
sage: [P,Q] = [E(-1,1),E(0,-1)]
sage: P.height(precision=100)
0.68666708330558658572355210295
sage: (3*Q).height(precision=100)/Q.height(precision=100)
9.0000000000000000000000000000
sage: _.parent()
Real Field with 100 bits of precision
Canonical heights over number fields are implemented as well:
sage: R.<x> = QQ[]
sage: K.<a> = NumberField(x^3-2)
sage: E = EllipticCurve([a, 4]); E
Elliptic Curve defined by y^2 = x^3 + a*x + 4 over Number Field in a with defining polynomial x^3 - 2
sage: P = E((0,2))
sage: P.height()
0.810463096585925
sage: P.height(precision=100)
0.81046309658592536863991810577
sage: P.height(precision=200)
0.81046309658592536863991810576865158896130286417155832378086
sage: (2*P).height() / P.height()
4.00000000000000
sage: (100*P).height() / P.height()
10000.0000000000
Setting normalised=False multiplies the height by the degree of :
sage: E = EllipticCurve('37a')
sage: P = E([0,0])
sage: P.height()
0.0511114082399688
sage: P.height(normalised=False)
0.0511114082399688
sage: K.<z> = CyclotomicField(5)
sage: EK = E.change_ring(K)
sage: PK = EK([0,0])
sage: PK.height()
0.0511114082399688
sage: PK.height(normalised=False)
0.204445632959875
Some consistency checks:
sage: E = EllipticCurve('5077a1')
sage: P = E([-2,3,1])
sage: P.height()
1.36857250535393
sage: EK = E.change_ring(QuadraticField(-3,'a'))
sage: PK = EK([-2,3,1])
sage: PK.height()
1.36857250535393
sage: K.<i> = NumberField(x^2+1)
sage: E = EllipticCurve(K, [0,0,4,6*i,0])
sage: Q = E.lift_x(-9/4); Q
(-9/4 : -27/8*i : 1)
sage: Q.height()
2.69518560017909
sage: (15*Q).height() / Q.height()
225.000000000000
sage: E = EllipticCurve('37a')
sage: P = E([0,-1])
sage: P.height()
0.0511114082399688
sage: K.<a> = QuadraticField(-7)
sage: ED = E.quadratic_twist(-7)
sage: Q = E.isomorphism_to(ED.change_ring(K))(P); Q
(0 : -7/2*a - 1/2 : 1)
sage: Q.height()
0.0511114082399688
sage: Q.height(precision=100)
0.051111408239968840235886099757
An example to show that the bug at trac ticket #5252 is fixed:
sage: E = EllipticCurve([1, -1, 1, -2063758701246626370773726978, 32838647793306133075103747085833809114881])
sage: P = E([-30987785091199, 258909576181697016447])
sage: P.height()
25.8603170675462
sage: P.height(precision=100)
25.860317067546190743868840741
sage: P.height(precision=250)
25.860317067546190743868840740735110323098872903844416215577171041783572513
sage: P.height(precision=500)
25.8603170675461907438688407407351103230988729038444162155771710417835725129551130570889813281792157278507639909972112856019190236125362914195452321720
sage: P.height(precision=100) == P.non_archimedean_local_height(prec=100)+P.archimedean_local_height(prec=100)
True
An example to show that the bug at trac ticket #8319 is fixed (correct height when the curve is not minimal):
sage: E = EllipticCurve([-5580472329446114952805505804593498080000,-157339733785368110382973689903536054787700497223306368000000])
sage: xP = 204885147732879546487576840131729064308289385547094673627174585676211859152978311600/23625501907057948132262217188983681204856907657753178415430361
sage: P = E.lift_x(xP)
sage: P.height()
157.432598516754
sage: Q = 2*P
sage: Q.height() # long time (4s)
629.730394067016
sage: Q.height()-4*P.height() # long time
0.000000000000000
An example to show that the bug at trac ticket #12509 is fixed (precision issues):
sage: x = polygen(QQ)
sage: K.<a> = NumberField(x^2-x-1)
sage: v = [0, a + 1, 1, 28665*a - 46382, 2797026*a - 4525688]
sage: E = EllipticCurve(v)
sage: P = E([72*a - 509/5, -682/25*a - 434/25])
sage: P.height()
1.38877711688727
sage: (2*P).height()/P.height()
4.00000000000000
sage: (2*P).height(precision=100)/P.height(precision=100)
4.0000000000000000000000000000
sage: (2*P).height(precision=1000)/P.height(precision=1000)
4.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
This shows that the bug reported at trac ticket #13951 has been fixed:
sage: E = EllipticCurve([0,17])
sage: P1 = E(2,5)
sage: P1.height()
1.06248137652528
sage: F = E.change_ring(QuadraticField(-3,'a'))
sage: P2 = F([2,5])
sage: P2.height()
1.06248137652528
Returns True iff this point is on the identity component of its curve with respect to a given (real or complex) embedding.
INPUT:
OUTPUT:
(bool) – True iff the point is on the identity component of the curve. (If the point is zero then the result is True.)
EXAMPLES:
For there is no need to specify an embedding:
sage: E=EllipticCurve('5077a1')
sage: [E.lift_x(x).is_on_identity_component() for x in range(-3,5)]
[False, False, False, False, False, True, True, True]
An example over a field with two real embeddings:
sage: L.<a> = QuadraticField(2)
sage: E=EllipticCurve(L,[0,1,0,a,a])
sage: P=E(-1,0)
sage: [P.is_on_identity_component(e) for e in L.embeddings(RR)]
[False, True]
We can check this as follows:
sage: [e(E.discriminant())>0 for e in L.embeddings(RR)]
[True, False]
sage: e = L.embeddings(RR)[0]
sage: E1 = EllipticCurve(RR,[e(ai) for ai in E.ainvs()])
sage: e1,e2,e3 = E1.two_division_polynomial().roots(RR,multiplicities=False)
sage: e1 < e2 < e3 and e(P[0]) < e3
True
Compute the local height of self at the non-archimedean place .
INPUT:
OUTPUT:
A real number. The normalisation is twice that in Silverman’s paper [Sil1988]. Note that this local height depends on the model of the curve.
ALGORITHM:
See [Sil1988], Section 5.
EXAMPLES:
Examples 2 and 3 from [Sil1988]:
sage: K.<i> = NumberField(x^2+1)
sage: E = EllipticCurve(K, [0,0,4,6*i,0]); E
Elliptic Curve defined by y^2 + 4*y = x^3 + 6*i*x over Number Field in i with defining polynomial x^2 + 1
sage: P = E((0,0))
sage: P.non_archimedean_local_height(K.ideal(i+1))
-1/2*log(2)
sage: P.non_archimedean_local_height(K.ideal(3))
0
sage: P.non_archimedean_local_height(K.ideal(1-2*i))
0
sage: Q = E.lift_x(-9/4); Q
(-9/4 : -27/8*i : 1)
sage: Q.non_archimedean_local_height(K.ideal(1+i))
2*log(2)
sage: Q.non_archimedean_local_height(K.ideal(3))
0
sage: Q.non_archimedean_local_height(K.ideal(1-2*i))
0
sage: Q.non_archimedean_local_height()
1/2*log(16)
An example over the rational numbers:
sage: E = EllipticCurve([0, 0, 0, -36, 0])
sage: P = E([-3, 9])
sage: P.non_archimedean_local_height()
-log(3)
Local heights of torsion points can be non-zero (unlike the global height):
sage: K.<i> = QuadraticField(-1)
sage: E = EllipticCurve([0, 0, 0, K(1), 0])
sage: P = E(i, 0)
sage: P.non_archimedean_local_height()
-1/2*log(2)
TESTS:
sage: Q.non_archimedean_local_height(prec=100)
1.3862943611198906188344642429
sage: (3*Q).non_archimedean_local_height()
1/2*log(75923153929839865104)
sage: F.<a> = NumberField(x^4 + 2*x^3 + 19*x^2 + 18*x + 288)
sage: F.ring_of_integers().gens()
[1, 5/6*a^3 + 1/6*a, 1/6*a^3 + 1/6*a^2, a^3]
sage: F.class_number()
12
sage: E = EllipticCurve('37a').change_ring(F)
sage: P = E((-a^2/6 - a/6 - 1, a)); P
(-1/6*a^2 - 1/6*a - 1 : a : 1)
sage: P[0].is_integral()
True
sage: P.non_archimedean_local_height()
0
This shows that the bug reported at trac ticket #13951 has been fixed:
sage: E = EllipticCurve([0,17])
sage: P = E(2,5)
sage: P.non_archimedean_local_height(2)
-2/3*log(2)
Deprecated: Use non_archimedean_local_height() instead. See trac ticket #13951 for details.
Return the order of this point on the elliptic curve.
If the point has infinite order, returns +Infinity. For
curves defined over , we call PARI; over other
number fields we implement the function here.
Note
additive_order() is a synonym for order()
EXAMPLES:
sage: E = EllipticCurve([0,0,1,-1,0])
sage: P = E([0,0]); P
(0 : 0 : 1)
sage: P.order()
+Infinity
sage: E = EllipticCurve([0,1])
sage: P = E([-1,0])
sage: P.order()
2
sage: P.additive_order()
2
Computes the -adic elliptic logarithm of this point.
INPUT:
p - integer: a prime absprec - integer (default: 20):
the initial -adic absolute precision of the computation
OUTPUT:
The -adic elliptic logarithm of self, with precision absprec.
AUTHORS:
ALGORITHM:
For points in the formal group (i.e. not integral at ) we
take the log() function from the formal groups module and
evaluate it at
. Otherwise we first multiply the point
to get into the formal group, and divide the result
afterwards.
Todo
See comments at trac ticket #4805. Currently the absolute precision of the result may be less than the given value of absprec, and error-handling is imperfect.
EXAMPLES:
sage: E = EllipticCurve([0,1,1,-2,0])
sage: E(0).padic_elliptic_logarithm(3)
0
sage: P = E(0,0)
sage: P.padic_elliptic_logarithm(3)
2 + 2*3 + 3^3 + 2*3^7 + 3^8 + 3^9 + 3^11 + 3^15 + 2*3^17 + 3^18 + O(3^19)
sage: P.padic_elliptic_logarithm(3).lift()
660257522
sage: P = E(-11/9,28/27)
sage: [(2*P).padic_elliptic_logarithm(p)/P.padic_elliptic_logarithm(p) for p in prime_range(20)] # long time (3s)
[2 + O(2^19), 2 + O(3^20), 2 + O(5^19), 2 + O(7^19), 2 + O(11^19), 2 + O(13^19), 2 + O(17^19), 2 + O(19^19)]
sage: [(3*P).padic_elliptic_logarithm(p)/P.padic_elliptic_logarithm(p) for p in prime_range(12)] # long time (2s)
[1 + 2 + O(2^19), 3 + 3^20 + O(3^21), 3 + O(5^19), 3 + O(7^19), 3 + O(11^19)]
sage: [(5*P).padic_elliptic_logarithm(p)/P.padic_elliptic_logarithm(p) for p in prime_range(12)] # long time (2s)
[1 + 2^2 + O(2^19), 2 + 3 + O(3^20), 5 + O(5^19), 5 + O(7^19), 5 + O(11^19)]
An example which arose during reviewing trac ticket #4741:
sage: E = EllipticCurve('794a1')
sage: P = E(-1,2)
sage: P.padic_elliptic_logarithm(2) # default precision=20
2^4 + 2^5 + 2^6 + 2^8 + 2^9 + 2^13 + 2^14 + 2^15 + O(2^16)
sage: P.padic_elliptic_logarithm(2, absprec=30)
2^4 + 2^5 + 2^6 + 2^8 + 2^9 + 2^13 + 2^14 + 2^15 + 2^22 + 2^23 + 2^24 + O(2^26)
sage: P.padic_elliptic_logarithm(2, absprec=40)
2^4 + 2^5 + 2^6 + 2^8 + 2^9 + 2^13 + 2^14 + 2^15 + 2^22 + 2^23 + 2^24 + 2^28 + 2^29 + 2^31 + 2^34 + O(2^35)
This finds the reduction of a point on the elliptic curve
modulo the prime
.
INPUT:
OUTPUT:
The point reduced to be a point on the elliptic curve modulo .
EXAMPLES:
sage: E = EllipticCurve([1,2,3,4,0])
sage: P = E(0,0)
sage: P.reduction(5)
(0 : 0 : 1)
sage: Q = E(98,931)
sage: Q.reduction(5)
(3 : 1 : 1)
sage: Q.reduction(5).curve() == E.reduction(5)
True
sage: F.<a> = NumberField(x^2+5)
sage: E = EllipticCurve(F,[1,2,3,4,0])
sage: Q = E(98,931)
sage: Q.reduction(a)
(3 : 1 : 1)
sage: Q.reduction(11)
(10 : 7 : 1)
sage: F.<a> = NumberField(x^3+x^2+1)
sage: E = EllipticCurve(F,[a,2])
sage: P = E(a,1)
sage: P.reduction(F.ideal(5))
(abar : 1 : 1)
sage: P.reduction(F.ideal(a^2-4*a-2))
(abar : 1 : 1)