AUTHORS:
Nick Alexander: original implementation over \(\QQ\)
Chris Wuthrich: original implementation over number fields
polynomials, added some features, unified Number Field and \(\QQ\) code.
Bases: sage.groups.additive_abelian.additive_abelian_wrapper.AdditiveAbelianGroupWrapper
The torsion subgroup of an elliptic curve over a number field.
EXAMPLES:
Examples over \(\QQ\):
sage: E = EllipticCurve([-4, 0]); E
Elliptic Curve defined by y^2 = x^3 - 4*x over Rational Field
sage: G = E.torsion_subgroup(); G
Torsion Subgroup isomorphic to Z/2 + Z/2 associated to the Elliptic Curve defined by y^2 = x^3 - 4*x over Rational Field
sage: G.order()
4
sage: G.gen(0)
(2 : 0 : 1)
sage: G.gen(1)
(0 : 0 : 1)
sage: G.ngens()
2
sage: E = EllipticCurve([17, -120, -60, 0, 0]); E
Elliptic Curve defined by y^2 + 17*x*y - 60*y = x^3 - 120*x^2 over Rational Field
sage: G = E.torsion_subgroup(); G
Torsion Subgroup isomorphic to Trivial group associated to the Elliptic Curve defined by y^2 + 17*x*y - 60*y = x^3 - 120*x^2 over Rational Field
sage: G.gens()
()
sage: e = EllipticCurve([0, 33076156654533652066609946884,0,\
347897536144342179642120321790729023127716119338758604800,\
1141128154369274295519023032806804247788154621049857648870032370285851781352816640000])
sage: e.torsion_order()
16
Constructing points from the torsion subgroup:
sage: E = EllipticCurve('14a1')
sage: T = E.torsion_subgroup()
sage: [E(t) for t in T]
[(0 : 1 : 0),
(9 : 23 : 1),
(2 : 2 : 1),
(1 : -1 : 1),
(2 : -5 : 1),
(9 : -33 : 1)]
An example where the torsion subgroup is not cyclic:
sage: E = EllipticCurve([0,0,0,-49,0])
sage: T = E.torsion_subgroup()
sage: [E(t) for t in T]
[(0 : 1 : 0), (7 : 0 : 1), (0 : 0 : 1), (-7 : 0 : 1)]
An example where the torsion subgroup is trivial:
sage: E = EllipticCurve('37a1')
sage: T = E.torsion_subgroup()
sage: T
Torsion Subgroup isomorphic to Trivial group associated to the Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
sage: [E(t) for t in T]
[(0 : 1 : 0)]
Examples over other Number Fields:
sage: E=EllipticCurve('11a1')
sage: K.<i>=NumberField(x^2+1)
sage: EK=E.change_ring(K)
sage: from sage.schemes.elliptic_curves.ell_torsion import EllipticCurveTorsionSubgroup
sage: EllipticCurveTorsionSubgroup(EK)
Torsion Subgroup isomorphic to Z/5 associated to the Elliptic Curve defined by y^2 + y = x^3 + (-1)*x^2 + (-10)*x + (-20) over Number Field in i with defining polynomial x^2 + 1
sage: E=EllipticCurve('11a1')
sage: K.<i>=NumberField(x^2+1)
sage: EK=E.change_ring(K)
sage: T = EK.torsion_subgroup()
sage: T.ngens()
1
sage: T.gen(0)
(5 : -6 : 1)
Note: this class is normally constructed indirectly as follows:
sage: T = EK.torsion_subgroup(); T
Torsion Subgroup isomorphic to Z/5 associated to the Elliptic Curve defined by y^2 + y = x^3 + (-1)*x^2 + (-10)*x + (-20) over Number Field in i with defining polynomial x^2 + 1
sage: type(T)
<class 'sage.schemes.elliptic_curves.ell_torsion.EllipticCurveTorsionSubgroup_with_category'>
AUTHORS:
Return the curve of this torsion subgroup.
EXAMPLES:
sage: E=EllipticCurve('11a1')
sage: K.<i>=NumberField(x^2+1)
sage: EK=E.change_ring(K)
sage: T = EK.torsion_subgroup()
sage: T.curve() is EK
True
Return a list of all the points in this torsion subgroup. The list is cached.
EXAMPLES:
sage: K.<i>=NumberField(x^2 + 1)
sage: E = EllipticCurve(K,[0,0,0,1,0])
sage: tor = E.torsion_subgroup()
sage: tor.points()
[(0 : 1 : 0), (-i : 0 : 1), (0 : 0 : 1), (i : 0 : 1)]