Exemplo n.º 1
0
def EllipticCurve(x=None, y=None, j=None, minimal_twist=True):
    r"""
    There are several ways to construct an elliptic curve:
    
    .. math::
    
       y^2 + a_1 xy + a_3 y = x^3 + a_2 x^2 + a_4 x + a_6.       
    
    
    - EllipticCurve([a1,a2,a3,a4,a6]): Elliptic curve with given
      a-invariants. The invariants are coerced into the parent of the
      first element. If all are integers, they are coerced into the
      rational numbers.
    
    - EllipticCurve([a4,a6]): Same as above, but a1=a2=a3=0.
    
    - EllipticCurve(label): Returns the elliptic curve over Q from the
      Cremona database with the given label. The label is a string, such
      as "11a" or "37b2". The letters in the label *must* be lower case
      (Cremona's new labeling).
    
    - EllipticCurve(R, [a1,a2,a3,a4,a6]): Create the elliptic curve
      over R with given a-invariants. Here R can be an arbitrary ring.
      Note that addition need not be defined.
    
            
    - EllipticCurve(j=j0) or EllipticCurve_from_j(j0): Return an
      elliptic curve with j-invariant `j0`.

    In each case above where the input is a list of length 2 or 5, one
    can instead give a 2 or 5-tuple instead.
    
    EXAMPLES: We illustrate creating elliptic curves.
    
    ::
    
        sage: EllipticCurve([0,0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
    
    We create a curve from a Cremona label::
    
        sage: EllipticCurve('37b2')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 1873*x - 31833 over Rational Field
        sage: EllipticCurve('5077a')
        Elliptic Curve defined by y^2 + y = x^3 - 7*x + 6 over Rational Field
        sage: EllipticCurve('389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field

    Old Cremona labels are allowed::

        sage: EllipticCurve('2400FF')
        Elliptic Curve defined by y^2 = x^3 + x^2 + 2*x + 8 over Rational Field

    Unicode labels are allowed::

        sage: EllipticCurve(u'389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field

    We create curves over a finite field as follows::

        sage: EllipticCurve([GF(5)(0),0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5
        sage: EllipticCurve(GF(5), [0, 0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5

    Elliptic curves over `\ZZ/N\ZZ` with `N` prime are of type
    "elliptic curve over a finite field"::

        sage: F = Zmod(101)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 101
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_finite_field.EllipticCurve_finite_field_with_category'>
        sage: E.category()
        Category of schemes over Ring of integers modulo 101

    In contrast, elliptic curves over `\ZZ/N\ZZ` with `N` composite
    are of type "generic elliptic curve"::

        sage: F = Zmod(95)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 95
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_generic.EllipticCurve_generic_with_category'>
        sage: E.category()
        Category of schemes over Ring of integers modulo 95

    The following is a curve over the complex numbers::
    
        sage: E = EllipticCurve(CC, [0,0,1,-1,0])
        sage: E
        Elliptic Curve defined by y^2 + 1.00000000000000*y = x^3 + (-1.00000000000000)*x over Complex Field with 53 bits of precision
        sage: E.j_invariant()
        2988.97297297297
    
    We can also create elliptic curves by giving the Weierstrass equation::
    
        sage: x, y = var('x,y')
        sage: EllipticCurve(y^2 + y ==  x^3 + x - 9)
        Elliptic Curve defined by y^2 + y = x^3 + x - 9 over Rational Field
        
        sage: R.<x,y> = GF(5)[]
        sage: EllipticCurve(x^3 + x^2 + 2 - y^2 - y*x)
        Elliptic Curve defined by y^2 + x*y  = x^3 + x^2 + 2 over Finite Field of size 5

    We can explicitly specify the `j`-invariant::

        sage: E = EllipticCurve(j=1728); E; E.j_invariant(); E.label()
        Elliptic Curve defined by y^2 = x^3 - x over Rational Field
        1728
        '32a2'

        sage: E = EllipticCurve(j=GF(5)(2)); E; E.j_invariant()
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Finite Field of size 5
        2

    See trac #6657::

        sage: EllipticCurve(GF(144169),j=1728)
        Elliptic Curve defined by y^2 = x^3 + x over Finite Field of size 144169

    By default, when a rational value of `j` is given, the constructed
    curve is a minimal twist (minimal conductor for curves with that
    `j`-invariant).  This can be changed by setting the optional
    parameter ``minimal_twist``, which is True by default, to False::


        sage: EllipticCurve(j=100)
        Elliptic Curve defined by y^2 = x^3 + x^2 + 3392*x + 307888 over Rational Field
        sage: E =EllipticCurve(j=100); E
        Elliptic Curve defined by y^2 = x^3 + x^2 + 3392*x + 307888 over Rational Field
        sage: E.conductor()
        33129800
        sage: E.j_invariant()
        100
        sage: E =EllipticCurve(j=100, minimal_twist=False); E
        Elliptic Curve defined by y^2 = x^3 + 488400*x - 530076800 over Rational Field
        sage: E.conductor()
        298168200
        sage: E.j_invariant()
        100

    Without this option, constructing the curve could take a long time
    since both `j` and `j-1728` have to be factored to compute the
    minimal twist (see :trac:`13100`)::

       sage: E = EllipticCurve_from_j(2^256+1,minimal_twist=False)
       sage: E.j_invariant() == 2^256+1
       True

    TESTS::

        sage: R = ZZ['u', 'v']
        sage: EllipticCurve(R, [1,1])
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Multivariate Polynomial Ring in u, v
        over Integer Ring
    
    We create a curve and a point over QQbar (see #6879)::
    
        sage: E = EllipticCurve(QQbar,[0,1])
        sage: E(0)
        (0 : 1 : 0)
        sage: E.base_field()
        Algebraic Field

        sage: E = EllipticCurve(RR,[1,2]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: EllipticCurve(CC,[3,4]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 3.00000000000000*x + 4.00000000000000 over Complex Field with 53 bits of precision
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: E = EllipticCurve(QQbar,[5,6]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 5*x + 6 over Algebraic Field
        Algebraic Field

    See trac #6657::

        sage: EllipticCurve(3,j=1728)
        Traceback (most recent call last):
        ...
        ValueError: First parameter (if present) must be a ring when j is specified

        sage: EllipticCurve(GF(5),j=3/5)
        Traceback (most recent call last):
        ...
        ValueError: First parameter must be a ring containing 3/5

    If the universe of the coefficients is a general field, the object
    constructed has type EllipticCurve_field.  Otherwise it is
    EllipticCurve_generic.  See trac #9816::

        sage: E = EllipticCurve([QQbar(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + x + 3 over Algebraic Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>

        sage: E = EllipticCurve([RR(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 3.00000000000000 over Real Field with 53 bits of precision
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>

        sage: E = EllipticCurve([i,i]); E
        Elliptic Curve defined by y^2 = x^3 + I*x + I over Symbolic Ring
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>
        sage: E.category()
        Category of schemes over Symbolic Ring
        sage: SR in Fields()
        True

        sage: F = FractionField(PolynomialRing(QQ,'t'))
        sage: t = F.gen()
        sage: E = EllipticCurve([t,0]); E
        Elliptic Curve defined by y^2 = x^3 + t*x over Fraction Field of Univariate Polynomial Ring in t over Rational Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>
        sage: E.category()
        Category of schemes over Fraction Field of Univariate Polynomial Ring in t over Rational Field

    See :trac:`12517`::

        sage: E = EllipticCurve([1..5])
        sage: EllipticCurve(E.a_invariants())
        Elliptic Curve defined by y^2 + x*y + 3*y = x^3 + 2*x^2 + 4*x + 5 over Rational Field

    See :trac:`11773`::

        sage: E = EllipticCurve()
        Traceback (most recent call last):
        ...
        TypeError: invalid input to EllipticCurve constructor

    """
    import ell_generic, ell_field, ell_finite_field, ell_number_field, ell_rational_field, ell_padic_field  # here to avoid circular includes
    
    if j is not None:
        if not x is None:
            if rings.is_Ring(x):
                try:
                    j = x(j)
                except (ZeroDivisionError, ValueError, TypeError):
                    raise ValueError, "First parameter must be a ring containing %s"%j
            else:
                raise ValueError, "First parameter (if present) must be a ring when j is specified"
        return EllipticCurve_from_j(j, minimal_twist)

    if x is None:
        raise TypeError, "invalid input to EllipticCurve constructor"
    
    if is_SymbolicEquation(x):
        x = x.lhs() - x.rhs()
    
    if parent(x) is SR:
        x = x._polynomial_(rings.QQ['x', 'y'])
    
    if rings.is_MPolynomial(x) and y is None:
        f = x
        if f.degree() != 3:
            raise ValueError, "Elliptic curves must be defined by a cubic polynomial."
        if f.degrees() == (3,2):
            x, y = f.parent().gens()
        elif f.degree() == (2,3):
            y, x = f.parent().gens()
        elif len(f.parent().gens()) == 2 or len(f.parent().gens()) == 3 and f.is_homogeneous():
            # We'd need a point too...
            raise NotImplementedError, "Construction of an elliptic curve from a generic cubic not yet implemented."
        else:
            raise ValueError, "Defining polynomial must be a cubic polynomial in two variables."

        try:
            if f.coefficient(x**3) < 0:
                f = -f
            # is there a nicer way to extract the coefficients?
            a1 = a2 = a3 = a4 = a6 = 0
            for coeff, mon in f:
                if mon == x**3:
                    assert coeff == 1
                elif mon == x**2:
                    a2 = coeff
                elif mon == x:
                    a4 = coeff
                elif mon == 1:
                    a6 = coeff
                elif mon == y**2:
                    assert coeff == -1
                elif mon == x*y:
                    a1 = -coeff
                elif mon == y:
                    a3 = -coeff
                else:
                    assert False
            return EllipticCurve([a1, a2, a3, a4, a6])
        except AssertionError:
            raise NotImplementedError, "Construction of an elliptic curve from a generic cubic not yet implemented."
    
    if rings.is_Ring(x):
        if rings.is_RationalField(x):
            return ell_rational_field.EllipticCurve_rational_field(x, y)
        elif rings.is_FiniteField(x) or (rings.is_IntegerModRing(x) and x.characteristic().is_prime()):
            return ell_finite_field.EllipticCurve_finite_field(x, y)
        elif rings.is_pAdicField(x):
            return ell_padic_field.EllipticCurve_padic_field(x, y)
        elif rings.is_NumberField(x):
            return ell_number_field.EllipticCurve_number_field(x, y)
        elif x in _Fields:
            return ell_field.EllipticCurve_field(x, y)
        return ell_generic.EllipticCurve_generic(x, y)

    if isinstance(x, unicode):
        x = str(x)

    if isinstance(x, str):
        return ell_rational_field.EllipticCurve_rational_field(x)

    if rings.is_RingElement(x) and y is None:
        raise TypeError, "invalid input to EllipticCurve constructor"

    if not isinstance(x, (list, tuple)):
        raise TypeError, "invalid input to EllipticCurve constructor"

    x = Sequence(x)
    if not (len(x) in [2,5]):
        raise ValueError, "sequence of coefficients must have length 2 or 5"
    R = x.universe()

    if isinstance(x[0], (rings.Rational, rings.Integer, int, long)):
        return ell_rational_field.EllipticCurve_rational_field(x, y)

    elif rings.is_NumberField(R):
        return ell_number_field.EllipticCurve_number_field(x, y)

    elif rings.is_pAdicField(R):
        return ell_padic_field.EllipticCurve_padic_field(x, y)
    
    elif rings.is_FiniteField(R) or (rings.is_IntegerModRing(R) and R.characteristic().is_prime()):
        return ell_finite_field.EllipticCurve_finite_field(x, y)

    elif R in _Fields:
        return ell_field.EllipticCurve_field(x, y)

    return ell_generic.EllipticCurve_generic(x, y)
Exemplo n.º 2
0
def EllipticCurve(x=None, y=None, j=None, minimal_twist=True):
    r"""
    Construct an elliptic curve.

    In Sage, an elliptic curve is always specified by its a-invariants

    .. math::

       y^2 + a_1 xy + a_3 y = x^3 + a_2 x^2 + a_4 x + a_6.

    INPUT:

    There are several ways to construct an elliptic curve:

    - ``EllipticCurve([a1,a2,a3,a4,a6])``: Elliptic curve with given
      a-invariants. The invariants are coerced into the parent of the
      first element. If all are integers, they are coerced into the
      rational numbers.

    - ``EllipticCurve([a4,a6])``: Same as above, but `a_1=a_2=a_3=0`.

    - ``EllipticCurve(label)``: Returns the elliptic curve over Q from
      the Cremona database with the given label. The label is a
      string, such as ``"11a"`` or ``"37b2"``. The letters in the
      label *must* be lower case (Cremona's new labeling).

    - ``EllipticCurve(R, [a1,a2,a3,a4,a6])``: Create the elliptic
      curve over ``R`` with given a-invariants. Here ``R`` can be an
      arbitrary ring. Note that addition need not be defined.

    - ``EllipticCurve(j=j0)`` or ``EllipticCurve_from_j(j0)``: Return
      an elliptic curve with j-invariant ``j0``.

    - ``EllipticCurve(polynomial)``: Read off the a-invariants from
      the polynomial coefficients, see
      :func:`EllipticCurve_from_Weierstrass_polynomial`.

    In each case above where the input is a list of length 2 or 5, one
    can instead give a 2 or 5-tuple instead.

    EXAMPLES:

    We illustrate creating elliptic curves::

        sage: EllipticCurve([0,0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field

    We create a curve from a Cremona label::

        sage: EllipticCurve('37b2')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 1873*x - 31833 over Rational Field
        sage: EllipticCurve('5077a')
        Elliptic Curve defined by y^2 + y = x^3 - 7*x + 6 over Rational Field
        sage: EllipticCurve('389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field

    Old Cremona labels are allowed::

        sage: EllipticCurve('2400FF')
        Elliptic Curve defined by y^2 = x^3 + x^2 + 2*x + 8 over Rational Field

    Unicode labels are allowed::

        sage: EllipticCurve(u'389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field

    We create curves over a finite field as follows::

        sage: EllipticCurve([GF(5)(0),0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5
        sage: EllipticCurve(GF(5), [0, 0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5

    Elliptic curves over `\ZZ/N\ZZ` with `N` prime are of type
    "elliptic curve over a finite field"::

        sage: F = Zmod(101)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 101
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_finite_field.EllipticCurve_finite_field_with_category'>
        sage: E.category()
        Category of schemes over Ring of integers modulo 101

    In contrast, elliptic curves over `\ZZ/N\ZZ` with `N` composite
    are of type "generic elliptic curve"::

        sage: F = Zmod(95)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 95
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_generic.EllipticCurve_generic_with_category'>
        sage: E.category()
        Category of schemes over Ring of integers modulo 95

    The following is a curve over the complex numbers::

        sage: E = EllipticCurve(CC, [0,0,1,-1,0])
        sage: E
        Elliptic Curve defined by y^2 + 1.00000000000000*y = x^3 + (-1.00000000000000)*x over Complex Field with 53 bits of precision
        sage: E.j_invariant()
        2988.97297297297

    We can also create elliptic curves by giving the Weierstrass equation::

        sage: x, y = var('x,y')
        sage: EllipticCurve(y^2 + y ==  x^3 + x - 9)
        Elliptic Curve defined by y^2 + y = x^3 + x - 9 over Rational Field

        sage: R.<x,y> = GF(5)[]
        sage: EllipticCurve(x^3 + x^2 + 2 - y^2 - y*x)
        Elliptic Curve defined by y^2 + x*y  = x^3 + x^2 + 2 over Finite Field of size 5

    We can explicitly specify the `j`-invariant::

        sage: E = EllipticCurve(j=1728); E; E.j_invariant(); E.label()
        Elliptic Curve defined by y^2 = x^3 - x over Rational Field
        1728
        '32a2'

        sage: E = EllipticCurve(j=GF(5)(2)); E; E.j_invariant()
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Finite Field of size 5
        2

    See :trac:`6657` ::

        sage: EllipticCurve(GF(144169),j=1728)
        Elliptic Curve defined by y^2 = x^3 + x over Finite Field of size 144169

    By default, when a rational value of `j` is given, the constructed
    curve is a minimal twist (minimal conductor for curves with that
    `j`-invariant).  This can be changed by setting the optional
    parameter ``minimal_twist``, which is True by default, to False::


        sage: EllipticCurve(j=100)
        Elliptic Curve defined by y^2 = x^3 + x^2 + 3392*x + 307888 over Rational Field
        sage: E =EllipticCurve(j=100); E
        Elliptic Curve defined by y^2 = x^3 + x^2 + 3392*x + 307888 over Rational Field
        sage: E.conductor()
        33129800
        sage: E.j_invariant()
        100
        sage: E =EllipticCurve(j=100, minimal_twist=False); E
        Elliptic Curve defined by y^2 = x^3 + 488400*x - 530076800 over Rational Field
        sage: E.conductor()
        298168200
        sage: E.j_invariant()
        100

    Without this option, constructing the curve could take a long time
    since both `j` and `j-1728` have to be factored to compute the
    minimal twist (see :trac:`13100`)::

       sage: E = EllipticCurve_from_j(2^256+1,minimal_twist=False)
       sage: E.j_invariant() == 2^256+1
       True

    TESTS::

        sage: R = ZZ['u', 'v']
        sage: EllipticCurve(R, [1,1])
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Multivariate Polynomial Ring in u, v
        over Integer Ring

    We create a curve and a point over QQbar (see #6879)::

        sage: E = EllipticCurve(QQbar,[0,1])
        sage: E(0)
        (0 : 1 : 0)
        sage: E.base_field()
        Algebraic Field

        sage: E = EllipticCurve(RR,[1,2]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: EllipticCurve(CC,[3,4]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 3.00000000000000*x + 4.00000000000000 over Complex Field with 53 bits of precision
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: E = EllipticCurve(QQbar,[5,6]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 5*x + 6 over Algebraic Field
        Algebraic Field

    See :trac:`6657` ::

        sage: EllipticCurve(3,j=1728)
        Traceback (most recent call last):
        ...
        ValueError: First parameter (if present) must be a ring when j is specified

        sage: EllipticCurve(GF(5),j=3/5)
        Traceback (most recent call last):
        ...
        ValueError: First parameter must be a ring containing 3/5

    If the universe of the coefficients is a general field, the object
    constructed has type EllipticCurve_field.  Otherwise it is
    EllipticCurve_generic.  See :trac:`9816` ::

        sage: E = EllipticCurve([QQbar(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + x + 3 over Algebraic Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>

        sage: E = EllipticCurve([RR(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 3.00000000000000 over Real Field with 53 bits of precision
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>

        sage: E = EllipticCurve([i,i]); E
        Elliptic Curve defined by y^2 = x^3 + I*x + I over Symbolic Ring
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>
        sage: E.category()
        Category of schemes over Symbolic Ring
        sage: SR in Fields()
        True

        sage: F = FractionField(PolynomialRing(QQ,'t'))
        sage: t = F.gen()
        sage: E = EllipticCurve([t,0]); E
        Elliptic Curve defined by y^2 = x^3 + t*x over Fraction Field of Univariate Polynomial Ring in t over Rational Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>
        sage: E.category()
        Category of schemes over Fraction Field of Univariate Polynomial Ring in t over Rational Field

    See :trac:`12517`::

        sage: E = EllipticCurve([1..5])
        sage: EllipticCurve(E.a_invariants())
        Elliptic Curve defined by y^2 + x*y + 3*y = x^3 + 2*x^2 + 4*x + 5 over Rational Field

    See :trac:`11773`::

        sage: E = EllipticCurve()
        Traceback (most recent call last):
        ...
        TypeError: invalid input to EllipticCurve constructor

    """
    import ell_generic, ell_field, ell_finite_field, ell_number_field, ell_rational_field, ell_padic_field  # here to avoid circular includes

    if j is not None:
        if not x is None:
            if rings.is_Ring(x):
                try:
                    j = x(j)
                except (ZeroDivisionError, ValueError, TypeError):
                    raise ValueError, "First parameter must be a ring containing %s"%j
            else:
                raise ValueError, "First parameter (if present) must be a ring when j is specified"
        return EllipticCurve_from_j(j, minimal_twist)

    if x is None:
        raise TypeError, "invalid input to EllipticCurve constructor"

    if is_SymbolicEquation(x):
        x = x.lhs() - x.rhs()

    if parent(x) is SR:
        x = x._polynomial_(rings.QQ['x', 'y'])

    if rings.is_MPolynomial(x):
        if y is None:
            return EllipticCurve_from_Weierstrass_polynomial(x)
        else:
            return EllipticCurve_from_cubic(x, y, morphism=False)

    if rings.is_Ring(x):
        if rings.is_RationalField(x):
            return ell_rational_field.EllipticCurve_rational_field(x, y)
        elif rings.is_FiniteField(x) or (rings.is_IntegerModRing(x) and x.characteristic().is_prime()):
            return ell_finite_field.EllipticCurve_finite_field(x, y)
        elif rings.is_pAdicField(x):
            return ell_padic_field.EllipticCurve_padic_field(x, y)
        elif rings.is_NumberField(x):
            return ell_number_field.EllipticCurve_number_field(x, y)
        elif x in _Fields:
            return ell_field.EllipticCurve_field(x, y)
        return ell_generic.EllipticCurve_generic(x, y)

    if isinstance(x, unicode):
        x = str(x)

    if isinstance(x, basestring):
        return ell_rational_field.EllipticCurve_rational_field(x)

    if rings.is_RingElement(x) and y is None:
        raise TypeError, "invalid input to EllipticCurve constructor"

    if not isinstance(x, (list, tuple)):
        raise TypeError, "invalid input to EllipticCurve constructor"

    x = Sequence(x)
    if not (len(x) in [2,5]):
        raise ValueError, "sequence of coefficients must have length 2 or 5"
    R = x.universe()

    if isinstance(x[0], (rings.Rational, rings.Integer, int, long)):
        return ell_rational_field.EllipticCurve_rational_field(x, y)

    elif rings.is_NumberField(R):
        return ell_number_field.EllipticCurve_number_field(x, y)

    elif rings.is_pAdicField(R):
        return ell_padic_field.EllipticCurve_padic_field(x, y)

    elif rings.is_FiniteField(R) or (rings.is_IntegerModRing(R) and R.characteristic().is_prime()):
        return ell_finite_field.EllipticCurve_finite_field(x, y)

    elif R in _Fields:
        return ell_field.EllipticCurve_field(x, y)

    return ell_generic.EllipticCurve_generic(x, y)
Exemplo n.º 3
0
def lseries_dokchitser(E, prec=53):
    """
    Return the Dokchitser L-series object associated to the elliptic
    curve E, which may be defined over the rational numbers or a
    number field.  Also prec is the number of bits of precision to
    which evaluation of the L-series occurs.
    
    INPUT:
        - E -- elliptic curve over a number field (or QQ)
        - prec -- integer (default: 53) precision in *bits*

    OUTPUT:
        - Dokchitser L-function object
    
    EXAMPLES::

    A curve over Q(sqrt(5)), for which we have an optimized implementation::
    
        sage: from psage.ellcurve.lseries.lseries_nf import lseries_dokchitser
        sage: K.<a> = NumberField(x^2-x-1); E = EllipticCurve([0,-a,a,0,0])
        sage: L = lseries_dokchitser(E); L
        Dokchitser L-function of Elliptic Curve defined by y^2 + a*y = x^3 + (-a)*x^2 over Number Field in a with defining polynomial x^2 - x - 1
        sage: L(1)
        0.422214159001667
        sage: L.taylor_series(1,5)
        0.422214159001667 + 0.575883864741340*z - 0.102163426876721*z^2 - 0.158119743123727*z^3 + 0.120350687595265*z^4 + O(z^5)

    Higher precision::
    
        sage: L = lseries_dokchitser(E, 200)
        sage: L(1)
        0.42221415900166715092967967717023093014455137669360598558872

    A curve over Q(i)::

        sage: K.<i> = NumberField(x^2 + 1)
        sage: E = EllipticCurve(K, [1,0])
        sage: E.conductor().norm()
        256
        sage: L = lseries_dokchitser(E, 10)
        sage: L.taylor_series(1,5)
        0.86 + 0.58*z - 0.62*z^2 + 0.19*z^3 + 0.18*z^4 + O(z^5)

    More examples::

        sage: lseries_dokchitser(EllipticCurve([0,-1,1,0,0]), 10)(1)
        0.25
        sage: K.<i> = NumberField(x^2+1)
        sage: lseries_dokchitser(EllipticCurve(K, [0,-1,1,0,0]), 10)(1)
        0.37
        sage: K.<a> = NumberField(x^2-x-1)
        sage: lseries_dokchitser(EllipticCurve(K, [0,-1,1,0,0]), 10)(1)
        0.72

        sage: E = EllipticCurve([0,-1,1,0,0])
        sage: E.quadratic_twist(2).rank()
        1
        sage: K.<d> = NumberField(x^2-2)
        sage: L = lseries_dokchitser(EllipticCurve(K, [0,-1,1,0,0]), 10)
        sage: L(1)
        0
        sage: L.taylor_series(1, 5)
        0.58*z + 0.20*z^2 - 0.50*z^3 + 0.28*z^4 + O(z^5)

    You can use this function as an algorithm to compute the sign of the functional
    equation (global root number)::

        sage: E = EllipticCurve([1..5])
        sage: E.root_number()
        -1
        sage: L = lseries_dokchitser(E,32); L
        Dokchitser L-function of Elliptic Curve defined by y^2 + x*y = x^3 - x^2 + 4*x + 3 over Rational Field
        sage: L.eps
        -1

    Over QQ, this isn't so useful (since Sage has a root_number
    method), but over number fields it is very useful::

        sage: K.<a> = NumberField(x^2 - x - 1)
        sage: E1=EllipticCurve([0,-a-1,1,a,0]); E0 = EllipticCurve([0,-a,a,0,0])
        sage: lseries_dokchitser(E1, 16).eps
        -1
        sage: E1.rank()
        1
        sage: lseries_dokchitser(E0, 16).eps
        1
        sage: E0.rank()
        0
    """
    # The code assumes in various places that we have a global minimal model,
    # for example, in anlist_sqrt5 above.
    E = E.global_minimal_model()

    # Check that we're over a number field.
    K = E.base_field()
    if not is_NumberField(K):
        raise TypeError("base field must be a number field")

    # Compute norm of the conductor -- awkward because QQ elements have no norm method (they should).
    N = E.conductor()
    if K != QQ:
        N = N.norm()

    # We guess the sign epsilon in the functional equation to be +1
    # first.  If our guess is wrong then we just choose the other
    # possibility.
    epsilon = 1

    # Define the Dokchitser L-function object with all parameters set:
    L = Dokchitser(conductor=N * K.discriminant()**2,
                   gammaV=[0] * K.degree() + [1] * K.degree(),
                   weight=2,
                   eps=epsilon,
                   poles=[],
                   prec=prec)

    # Find out how many coefficients of the Dirichlet series are needed
    # to compute to the requested precision.
    n = L.num_coeffs()
    # print "num coeffs = %s"%n

    # Compute the Dirichlet series coefficients
    coeffs = anlist(E, n)[1:]

    # Define a string that when evaluated in PARI defines a function
    # a(k), which returns the Dirichlet coefficient a_k.
    s = 'v=%s; a(k)=v[k];' % coeffs

    # Actually tell the L-series / PARI about the coefficients.
    L.init_coeffs('a(k)', pari_precode=s)

    # Test that the functional equation is satisfied.  This will very,
    # very, very likely if we chose the sign of the functional
    # equation incorrectly, or made any mistake in computing the
    # Dirichlet series coefficients.
    tiny = max(1e-8, old_div(1.0, 2**(prec - 1)))
    if abs(L.check_functional_equation()) > tiny:
        # The test failed, so we try the other choice of functional equation.
        epsilon *= -1
        L.eps = epsilon

        # It is not necessary to recreate L -- just tell PARI the different sign.
        L._gp_eval('sgn = %s' % epsilon)

        # Once again, verify that the functional equation is
        # satisfied.  If it is, then we've got it.  If it isn't, then
        # there is definitely some other subtle bug, probably in computed
        # the Dirichlet series coefficients.
        if abs(L.check_functional_equation()) > tiny:
            raise RuntimeError(
                "Functional equation not numerically satisfied for either choice of sign"
            )

    L.rename('Dokchitser L-function of %s' % E)
    return L
Exemplo n.º 4
0
def check_prime(K, P):
    r"""
    Function to check that `P` determines a prime of `K`, and return that ideal.

    INPUT:

    - ``K`` -- a number field (including `\QQ`).

    - ``P`` -- an element of ``K`` or a (fractional) ideal of ``K``.

    OUTPUT:

    - If ``K`` is `\QQ`: the prime integer equal to or which generates `P`.

    - If ``K`` is not `\QQ`: the prime ideal equal to or generated by `P`.

    .. note::

       If `P` is not a prime and does not generate a prime, a TypeError is raised.

    EXAMPLES::

        sage: from sage.schemes.elliptic_curves.ell_local_data import check_prime
        sage: check_prime(QQ,3)
        3
        sage: check_prime(QQ,ZZ.ideal(31))
        31
        sage: K.<a>=NumberField(x^2-5)
        sage: check_prime(K,a)
        Fractional ideal (a)
        sage: check_prime(K,a+1)
        Fractional ideal (a + 1)
        sage: [check_prime(K,P) for P in K.primes_above(31)]
        [Fractional ideal (5/2*a + 1/2), Fractional ideal (5/2*a - 1/2)]
    """
    if K is QQ:
        if isinstance(P, (int, long, Integer)):
            P = Integer(P)
            if P.is_prime():
                return P
            else:
                raise TypeError, "%s is not prime" % P
        else:
            if is_Ideal(P) and P.base_ring() is ZZ and P.is_prime():
                return P.gen()
        raise TypeError, "%s is not a prime ideal of %s" % (P, ZZ)

    if not is_NumberField(K):
        raise TypeError, "%s is not a number field" % K

    if is_NumberFieldFractionalIdeal(P):
        if P.is_prime():
            return P
        else:
            raise TypeError, "%s is not a prime ideal of %s" % (P, K)

    if is_NumberFieldElement(P):
        if P in K:
            P = K.ideal(P)
        else:
            raise TypeError, "%s is not an element of %s" % (P, K)
        if P.is_prime():
            return P
        else:
            raise TypeError, "%s is not a prime ideal of %s" % (P, K)

    raise TypeError, "%s is not a valid prime of %s" % (P, K)
Exemplo n.º 5
0
def check_prime(K, P):
    r"""
    Function to check that `P` determines a prime of `K`, and return that ideal.

    INPUT:

    - ``K`` -- a number field (including `\QQ`).

    - ``P`` -- an element of ``K`` or a (fractional) ideal of ``K``.

    OUTPUT:

    - If ``K`` is `\QQ`: the prime integer equal to or which generates `P`.

    - If ``K`` is not `\QQ`: the prime ideal equal to or generated by `P`.

    .. note::

       If `P` is not a prime and does not generate a prime, a TypeError is raised.

    EXAMPLES::

        sage: from sage.schemes.elliptic_curves.ell_local_data import check_prime
        sage: check_prime(QQ,3)
        3
        sage: check_prime(QQ,ZZ.ideal(31))
        31
        sage: K.<a>=NumberField(x^2-5)
        sage: check_prime(K,a)
        Fractional ideal (a)
        sage: check_prime(K,a+1)
        Fractional ideal (a + 1)
        sage: [check_prime(K,P) for P in K.primes_above(31)]
        [Fractional ideal (5/2*a + 1/2), Fractional ideal (5/2*a - 1/2)]
    """
    if K is QQ:
        if isinstance(P, (int, long, Integer)):
            P = Integer(P)
            if P.is_prime():
                return P
            else:
                raise TypeError, "%s is not prime" % P
        else:
            if is_Ideal(P) and P.base_ring() is ZZ and P.is_prime():
                return P.gen()
        raise TypeError, "%s is not a prime ideal of %s" % (P, ZZ)

    if not is_NumberField(K):
        raise TypeError, "%s is not a number field" % K

    if is_NumberFieldFractionalIdeal(P):
        if P.is_prime():
            return P
        else:
            raise TypeError, "%s is not a prime ideal of %s" % (P, K)

    if is_NumberFieldElement(P):
        if P in K:
            P = K.ideal(P)
        else:
            raise TypeError, "%s is not an element of %s" % (P, K)
        if P.is_prime():
            return P
        else:
            raise TypeError, "%s is not a prime ideal of %s" % (P, K)

    raise TypeError, "%s is not a valid prime of %s" % (P, K)
Exemplo n.º 6
0
def EllipticCurve(x=None, y=None, j=None):
    r"""
    There are several ways to construct an elliptic curve:
    
    .. math::
    
       y^2 + a_1 xy + a_3 y = x^3 + a_2 x^2 + a_4 x + a_6.       
    
    
    - EllipticCurve([a1,a2,a3,a4,a6]): Elliptic curve with given
      a-invariants. The invariants are coerced into the parent of the
      first element. If all are integers, they are coerced into the
      rational numbers.
    
    - EllipticCurve([a4,a6]): Same as above, but a1=a2=a3=0.
    
    - EllipticCurve(label): Returns the elliptic curve over Q from the
      Cremona database with the given label. The label is a string, such
      as "11a" or "37b2". The letters in the label *must* be lower case
      (Cremona's new labeling).
    
    - EllipticCurve(R, [a1,a2,a3,a4,a6]): Create the elliptic curve
      over R with given a-invariants. Here R can be an arbitrary ring.
      Note that addition need not be defined.
    
            
    - EllipticCurve(j): Return an elliptic curve with j-invariant
      `j`.  Warning: this is deprecated.  Use ``EllipticCurve_from_j(j)`` 
      or ``EllipticCurve(j=j)`` instead.         

    In each case above where the input is a list of length 2 or 5, one
    can instead give a 2 or 5-tuple instead.
    
    EXAMPLES: We illustrate creating elliptic curves.
    
    ::
    
        sage: EllipticCurve([0,0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
    
    We create a curve from a Cremona label::
    
        sage: EllipticCurve('37b2')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 1873*x - 31833 over Rational Field
        sage: EllipticCurve('5077a')
        Elliptic Curve defined by y^2 + y = x^3 - 7*x + 6 over Rational Field
        sage: EllipticCurve('389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field

    Unicode labels are allowed::

        sage: EllipticCurve(u'389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field
    
    We create curves over a finite field as follows::
    
        sage: EllipticCurve([GF(5)(0),0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5
        sage: EllipticCurve(GF(5), [0, 0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5

    Elliptic curves over `\ZZ/N\ZZ` with `N` prime are of type
    "elliptic curve over a finite field"::

        sage: F = Zmod(101)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 101
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_finite_field.EllipticCurve_finite_field_with_category'>
        sage: E.category()
        Category of schemes over Ring of integers modulo 101

    In contrast, elliptic curves over `\ZZ/N\ZZ` with `N` composite
    are of type "generic elliptic curve"::

        sage: F = Zmod(95)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 95
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_generic.EllipticCurve_generic_with_category'>
        sage: E.category()
        Category of schemes over Ring of integers modulo 95

    The following is a curve over the complex numbers::
    
        sage: E = EllipticCurve(CC, [0,0,1,-1,0])
        sage: E
        Elliptic Curve defined by y^2 + 1.00000000000000*y = x^3 + (-1.00000000000000)*x over Complex Field with 53 bits of precision
        sage: E.j_invariant()
        2988.97297297297
    
    We can also create elliptic curves by giving the Weierstrass equation::
    
        sage: x, y = var('x,y')
        sage: EllipticCurve(y^2 + y ==  x^3 + x - 9)
        Elliptic Curve defined by y^2 + y = x^3 + x - 9 over Rational Field
        
        sage: R.<x,y> = GF(5)[]
        sage: EllipticCurve(x^3 + x^2 + 2 - y^2 - y*x)
        Elliptic Curve defined by y^2 + x*y  = x^3 + x^2 + 2 over Finite Field of size 5

    We can explicitly specify the `j`-invariant::

        sage: E = EllipticCurve(j=1728); E; E.j_invariant(); E.label()
        Elliptic Curve defined by y^2 = x^3 - x over Rational Field
        1728
        '32a2'

        sage: E = EllipticCurve(j=GF(5)(2)); E; E.j_invariant()
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Finite Field of size 5
        2

    See trac #6657::    

        sage: EllipticCurve(GF(144169),j=1728)
        Elliptic Curve defined by y^2 = x^3 + x over Finite Field of size 144169


    TESTS::
    
        sage: R = ZZ['u', 'v']
        sage: EllipticCurve(R, [1,1])
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Multivariate Polynomial Ring in u, v
        over Integer Ring
    
    We create a curve and a point over QQbar (see #6879)::
    
        sage: E = EllipticCurve(QQbar,[0,1])
        sage: E(0)
        (0 : 1 : 0)
        sage: E.base_field()
        Algebraic Field

        sage: E = EllipticCurve(RR,[1,2]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: EllipticCurve(CC,[3,4]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 3.00000000000000*x + 4.00000000000000 over Complex Field with 53 bits of precision
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: E = EllipticCurve(QQbar,[5,6]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 5*x + 6 over Algebraic Field
        Algebraic Field

    See trac #6657::

        sage: EllipticCurve(3,j=1728)
        Traceback (most recent call last):
        ...
        ValueError: First parameter (if present) must be a ring when j is specified

        sage: EllipticCurve(GF(5),j=3/5)
        Traceback (most recent call last):
        ...
        ValueError: First parameter must be a ring containing 3/5

    If the universe of the coefficients is a general field, the object
    constructed has type EllipticCurve_field.  Otherwise it is
    EllipticCurve_generic.  See trac #9816::

        sage: E = EllipticCurve([QQbar(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + x + 3 over Algebraic Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>

        sage: E = EllipticCurve([RR(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 3.00000000000000 over Real Field with 53 bits of precision
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>

        sage: E = EllipticCurve([i,i]); E
        Elliptic Curve defined by y^2 = x^3 + I*x + I over Symbolic Ring
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>
        sage: E.category()
        Category of schemes over Symbolic Ring
        sage: is_field(SR)
        True

        sage: F = FractionField(PolynomialRing(QQ,'t'))
        sage: t = F.gen()
        sage: E = EllipticCurve([t,0]); E
        Elliptic Curve defined by y^2 = x^3 + t*x over Fraction Field of Univariate Polynomial Ring in t over Rational Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field_with_category'>
        sage: E.category()
        Category of schemes over Fraction Field of Univariate Polynomial Ring in t over Rational Field

    See :trac:`12517`::

        sage: E = EllipticCurve([1..5])
        sage: EllipticCurve(E.a_invariants())
        Elliptic Curve defined by y^2 + x*y + 3*y = x^3 + 2*x^2 + 4*x + 5 over Rational Field
    """
    import ell_generic, ell_field, ell_finite_field, ell_number_field, ell_rational_field, ell_padic_field  # here to avoid circular includes
    
    if j is not None:
        if not x is None:
            if rings.is_Ring(x):
                try:
                    j = x(j)
                except (ZeroDivisionError, ValueError, TypeError):                    
                    raise ValueError, "First parameter must be a ring containing %s"%j
            else:
                raise ValueError, "First parameter (if present) must be a ring when j is specified"
        return EllipticCurve_from_j(j)

    assert x is not None
    
    if is_SymbolicEquation(x):
        x = x.lhs() - x.rhs()
    
    if parent(x) is SR:
        x = x._polynomial_(rings.QQ['x', 'y'])
    
    if rings.is_MPolynomial(x) and y is None:
        f = x
        if f.degree() != 3:
            raise ValueError, "Elliptic curves must be defined by a cubic polynomial."
        if f.degrees() == (3,2):
            x, y = f.parent().gens()
        elif f.degree() == (2,3):
            y, x = f.parent().gens()
        elif len(f.parent().gens()) == 2 or len(f.parent().gens()) == 3 and f.is_homogeneous():
            # We'd need a point too...
            raise NotImplementedError, "Construction of an elliptic curve from a generic cubic not yet implemented."
        else:
            raise ValueError, "Defining polynomial must be a cubic polynomial in two variables."

        try:
            if f.coefficient(x**3) < 0:
                f = -f
            # is there a nicer way to extract the coefficients?
            a1 = a2 = a3 = a4 = a6 = 0
            for coeff, mon in f:
                if mon == x**3:
                    assert coeff == 1
                elif mon == x**2:
                    a2 = coeff
                elif mon == x:
                    a4 = coeff
                elif mon == 1:
                    a6 = coeff
                elif mon == y**2:
                    assert coeff == -1
                elif mon == x*y:
                    a1 = -coeff
                elif mon == y:
                    a3 = -coeff
                else:
                    assert False
            return EllipticCurve([a1, a2, a3, a4, a6])
        except AssertionError:
            raise NotImplementedError, "Construction of an elliptic curve from a generic cubic not yet implemented."
    
    if rings.is_Ring(x):
        if rings.is_RationalField(x):
            return ell_rational_field.EllipticCurve_rational_field(x, y)
        elif rings.is_FiniteField(x) or (rings.is_IntegerModRing(x) and x.characteristic().is_prime()):
            return ell_finite_field.EllipticCurve_finite_field(x, y)
        elif rings.is_pAdicField(x):
            return ell_padic_field.EllipticCurve_padic_field(x, y)
        elif rings.is_NumberField(x):
            return ell_number_field.EllipticCurve_number_field(x, y)
        elif rings.is_Field(x):
            return ell_field.EllipticCurve_field(x, y)
        return ell_generic.EllipticCurve_generic(x, y)

    if isinstance(x, unicode):
        x = str(x)
        
    if isinstance(x, str):
        return ell_rational_field.EllipticCurve_rational_field(x)
        
    if rings.is_RingElement(x) and y is None:
        from sage.misc.misc import deprecation
        deprecation("'EllipticCurve(j)' is deprecated; use 'EllipticCurve_from_j(j)' or 'EllipticCurve(j=j)' instead.")
        # Fixed for all characteristics and cases by John Cremona
        j=x
        F=j.parent().fraction_field()
        char=F.characteristic()
        if char==2:
            if j==0:
                return EllipticCurve(F, [ 0, 0, 1, 0, 0 ])
            else:
                return EllipticCurve(F, [ 1, 0, 0, 0, 1/j ])
        if char==3:
            if j==0:
                return EllipticCurve(F, [ 0, 0, 0, 1, 0 ])
            else:
                return EllipticCurve(F, [ 0, j, 0, 0, -j**2 ])
        if j == 0:
            return EllipticCurve(F, [ 0, 0, 0, 0, 1 ])
        if j == 1728:
            return EllipticCurve(F, [ 0, 0, 0, 1, 0 ])
        k=j-1728
        return EllipticCurve(F, [0,0,0,-3*j*k, -2*j*k**2])

    if not isinstance(x, (list, tuple)):
        raise TypeError, "invalid input to EllipticCurve constructor"

    x = Sequence(x)
    if not (len(x) in [2,5]):
        raise ValueError, "sequence of coefficients must have length 2 or 5"
    R = x.universe()

    if isinstance(x[0], (rings.Rational, rings.Integer, int, long)):
        return ell_rational_field.EllipticCurve_rational_field(x, y)

    elif rings.is_NumberField(R):
        return ell_number_field.EllipticCurve_number_field(x, y)

    elif rings.is_pAdicField(R):
        return ell_padic_field.EllipticCurve_padic_field(x, y)
    
    elif rings.is_FiniteField(R) or (rings.is_IntegerModRing(R) and R.characteristic().is_prime()):
        return ell_finite_field.EllipticCurve_finite_field(x, y)

    elif rings.is_Field(R):
        return ell_field.EllipticCurve_field(x, y)

    return ell_generic.EllipticCurve_generic(x, y)
Exemplo n.º 7
0
def lseries_dokchitser(E, prec=53):
    """
    Return the Dokchitser L-series object associated to the elliptic
    curve E, which may be defined over the rational numbers or a
    number field.  Also prec is the number of bits of precision to
    which evaluation of the L-series occurs.
    
    INPUT:
        - E -- elliptic curve over a number field (or QQ)
        - prec -- integer (default: 53) precision in *bits*

    OUTPUT:
        - Dokchitser L-function object
    
    EXAMPLES::

    A curve over Q(sqrt(5)), for which we have an optimized implementation::
    
        sage: from psage.ellcurve.lseries.lseries_nf import lseries_dokchitser
        sage: K.<a> = NumberField(x^2-x-1); E = EllipticCurve([0,-a,a,0,0])
        sage: L = lseries_dokchitser(E); L
        Dokchitser L-function of Elliptic Curve defined by y^2 + a*y = x^3 + (-a)*x^2 over Number Field in a with defining polynomial x^2 - x - 1
        sage: L(1)
        0.422214159001667
        sage: L.taylor_series(1,5)
        0.422214159001667 + 0.575883864741340*z - 0.102163426876721*z^2 - 0.158119743123727*z^3 + 0.120350687595265*z^4 + O(z^5)

    Higher precision::
    
        sage: L = lseries_dokchitser(E, 200)
        sage: L(1)
        0.42221415900166715092967967717023093014455137669360598558872

    A curve over Q(i)::

        sage: K.<i> = NumberField(x^2 + 1)
        sage: E = EllipticCurve(K, [1,0])
        sage: E.conductor().norm()
        256
        sage: L = lseries_dokchitser(E, 10)
        sage: L.taylor_series(1,5)
        0.86 + 0.58*z - 0.62*z^2 + 0.19*z^3 + 0.18*z^4 + O(z^5)

    More examples::

        sage: lseries_dokchitser(EllipticCurve([0,-1,1,0,0]), 10)(1)
        0.25
        sage: K.<i> = NumberField(x^2+1)
        sage: lseries_dokchitser(EllipticCurve(K, [0,-1,1,0,0]), 10)(1)
        0.37
        sage: K.<a> = NumberField(x^2-x-1)
        sage: lseries_dokchitser(EllipticCurve(K, [0,-1,1,0,0]), 10)(1)
        0.72

        sage: E = EllipticCurve([0,-1,1,0,0])
        sage: E.quadratic_twist(2).rank()
        1
        sage: K.<d> = NumberField(x^2-2)
        sage: L = lseries_dokchitser(EllipticCurve(K, [0,-1,1,0,0]), 10)
        sage: L(1)
        0
        sage: L.taylor_series(1, 5)
        0.58*z + 0.20*z^2 - 0.50*z^3 + 0.28*z^4 + O(z^5)

    You can use this function as an algorithm to compute the sign of the functional
    equation (global root number)::

        sage: E = EllipticCurve([1..5])
        sage: E.root_number()
        -1
        sage: L = lseries_dokchitser(E,32); L
        Dokchitser L-function of Elliptic Curve defined by y^2 + x*y = x^3 - x^2 + 4*x + 3 over Rational Field
        sage: L.eps
        -1

    Over QQ, this isn't so useful (since Sage has a root_number
    method), but over number fields it is very useful::

        sage: K.<a> = NumberField(x^2 - x - 1)
        sage: E1=EllipticCurve([0,-a-1,1,a,0]); E0 = EllipticCurve([0,-a,a,0,0])
        sage: lseries_dokchitser(E1, 16).eps
        -1
        sage: E1.rank()
        1
        sage: lseries_dokchitser(E0, 16).eps
        1
        sage: E0.rank()
        0
    """
    # The code asssumes in various places that we have a global minimal model,
    # for example, in anlist_sqrt5 above.
    E = E.global_minimal_model() 

    # Check that we're over a number field.
    K = E.base_field()
    if not is_NumberField(K):
        raise TypeError, "base field must be a number field"

    # Compute norm of the conductor -- awkward because QQ elements have no norm method (they should).
    N = E.conductor()
    if K != QQ:
        N = N.norm()

    # We guess the sign epsilon in the functional equation to be +1
    # first.  If our guess is wrong then we just choose the other
    # possibility.
    epsilon = 1

    # Define the Dokchitser L-function object with all parameters set:
    L = Dokchitser(conductor = N * K.discriminant()**2,
                   gammaV = [0]*K.degree() + [1]*K.degree(),
                   weight = 2, eps = epsilon, poles = [], prec = prec)

    # Find out how many coefficients of the Dirichlet series are needed
    # to compute to the requested precision.
    n = L.num_coeffs()
    # print "num coeffs = %s"%n


    # Compute the Dirichlet series coefficients
    coeffs = anlist(E, n)[1:]

    # Define a string that when evaluated in PARI defines a function
    # a(k), which returns the Dirichlet coefficient a_k.
    s = 'v=%s; a(k)=v[k];'%coeffs

    # Actually tell the L-series / PARI about the coefficients.
    L.init_coeffs('a(k)', pari_precode = s)      

    # Test that the functional equation is satisfied.  This will very,
    # very, very likely if we chose the sign of the functional
    # equation incorrectly, or made any mistake in computing the
    # Dirichlet series coefficients. 
    tiny = max(1e-8, 1.0/2**(prec-1))
    if abs(L.check_functional_equation()) > tiny:
        # The test failed, so we try the other choice of functional equation.
        epsilon *= -1
        L.eps = epsilon

        # It is not necessary to recreate L -- just tell PARI the different sign.
        L._gp_eval('sgn = %s'%epsilon)

        # Once again, verify that the functional equation is
        # satisfied.  If it is, then we've got it.  If it isn't, then
        # there is definitely some other subtle bug, probably in computed
        # the Dirichlet series coefficients.  
        if abs(L.check_functional_equation()) > tiny: 
            raise RuntimeError, "Functional equation not numerically satisfied for either choice of sign"
        
    L.rename('Dokchitser L-function of %s'%E)
    return L
Exemplo n.º 8
0
def EllipticCurve(x=None, y=None, j=None):
    r"""
    There are several ways to construct an elliptic curve:
    
    .. math::
    
       y^2 + a_1 xy + a_3 y = x^3 + a_2 x^2 + a_4 x + a_6.       
    
    
    - EllipticCurve([a1,a2,a3,a4,a6]): Elliptic curve with given
      a-invariants. The invariants are coerced into the parent of the
      first element. If all are integers, they are coerced into the
      rational numbers.
    
    - EllipticCurve([a4,a6]): Same as above, but a1=a2=a3=0.
    
    - EllipticCurve(label): Returns the elliptic curve over Q from the
      Cremona database with the given label. The label is a string, such
      as "11a" or "37b2". The letters in the label *must* be lower case
      (Cremona's new labeling).
    
    - EllipticCurve(R, [a1,a2,a3,a4,a6]): Create the elliptic curve
      over R with given a-invariants. Here R can be an arbitrary ring.
      Note that addition need not be defined.
    
            
    - EllipticCurve(j): Return an elliptic curve with j-invariant
      `j`.  Warning: this is deprecated.  Use ``EllipticCurve_from_j(j)`` 
      or ``EllipticCurve(j=j)`` instead.         

    
    EXAMPLES: We illustrate creating elliptic curves.
    
    ::
    
        sage: EllipticCurve([0,0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 - x over Rational Field
    
    We create a curve from a Cremona label::
    
        sage: EllipticCurve('37b2')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 1873*x - 31833 over Rational Field
        sage: EllipticCurve('5077a')
        Elliptic Curve defined by y^2 + y = x^3 - 7*x + 6 over Rational Field
        sage: EllipticCurve('389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field

    Unicode labels are allowed::

        sage: EllipticCurve(u'389a')
        Elliptic Curve defined by y^2 + y = x^3 + x^2 - 2*x over Rational Field
    
    We create curves over a finite field as follows::
    
        sage: EllipticCurve([GF(5)(0),0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5
        sage: EllipticCurve(GF(5), [0, 0,1,-1,0])
        Elliptic Curve defined by y^2 + y = x^3 + 4*x over Finite Field of size 5

    Elliptic curves over `\ZZ/N\ZZ` with `N` prime are of type
    "elliptic curve over a finite field"::

        sage: F = Zmod(101)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 101
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_finite_field.EllipticCurve_finite_field'>
            
    In contrast, elliptic curves over `\ZZ/N\ZZ` with `N` composite
    are of type "generic elliptic curve"::

        sage: F = Zmod(95)
        sage: EllipticCurve(F, [2, 3])
        Elliptic Curve defined by y^2 = x^3 + 2*x + 3 over Ring of integers modulo 95
        sage: E = EllipticCurve([F(2), F(3)])
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_generic.EllipticCurve_generic'>
    
    The following is a curve over the complex numbers::
    
        sage: E = EllipticCurve(CC, [0,0,1,-1,0])
        sage: E
        Elliptic Curve defined by y^2 + 1.00000000000000*y = x^3 + (-1.00000000000000)*x over Complex Field with 53 bits of precision
        sage: E.j_invariant()
        2988.97297297297
    
    We can also create elliptic curves by giving the Weierstrass equation::
    
        sage: x, y = var('x,y')
        sage: EllipticCurve(y^2 + y ==  x^3 + x - 9)
        Elliptic Curve defined by y^2 + y = x^3 + x - 9 over Rational Field
        
        sage: R.<x,y> = GF(5)[]
        sage: EllipticCurve(x^3 + x^2 + 2 - y^2 - y*x)
        Elliptic Curve defined by y^2 + x*y  = x^3 + x^2 + 2 over Finite Field of size 5

    We can explicitly specify the `j`-invariant::

        sage: E = EllipticCurve(j=1728); E; E.j_invariant(); E.label()
        Elliptic Curve defined by y^2 = x^3 - x over Rational Field
        1728
        '32a2'

        sage: E = EllipticCurve(j=GF(5)(2)); E; E.j_invariant()
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Finite Field of size 5
        2

    See trac #6657::    

        sage: EllipticCurve(GF(144169),j=1728)
        Elliptic Curve defined by y^2 = x^3 + x over Finite Field of size 144169


    TESTS::
    
        sage: R = ZZ['u', 'v']
        sage: EllipticCurve(R, [1,1])
        Elliptic Curve defined by y^2 = x^3 + x + 1 over Multivariate Polynomial Ring in u, v
        over Integer Ring
    
    We create a curve and a point over QQbar (see #6879)::
    
        sage: E = EllipticCurve(QQbar,[0,1])
        sage: E(0)
        (0 : 1 : 0)
        sage: E.base_field()
        Algebraic Field

        sage: E = EllipticCurve(RR,[1,2]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: EllipticCurve(CC,[3,4]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 3.00000000000000*x + 4.00000000000000 over Complex Field with 53 bits of precision
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 2.00000000000000 over Real Field with 53 bits of precision
        Real Field with 53 bits of precision
        sage: E = EllipticCurve(QQbar,[5,6]); E; E.base_field()
        Elliptic Curve defined by y^2 = x^3 + 5*x + 6 over Algebraic Field
        Algebraic Field

    See trac #6657::

        sage: EllipticCurve(3,j=1728)
        Traceback (most recent call last):
        ...
        ValueError: First parameter (if present) must be a ring when j is specified

        sage: EllipticCurve(GF(5),j=3/5)
        Traceback (most recent call last):
        ...
        ValueError: First parameter must be a ring containing 3/5

    If the universe of the coefficients is a general field, the object
    constructed has type EllipticCurve_field.  Otherwise it is
    EllipticCurve_generic.  See trac #9816::

        sage: E = EllipticCurve([QQbar(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + x + 3 over Algebraic Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field'>

        sage: E = EllipticCurve([RR(1),3]); E
        Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 3.00000000000000 over Real Field with 53 bits of precision
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field'>

        sage: E = EllipticCurve([i,i]); E
        Elliptic Curve defined by y^2 = x^3 + I*x + I over Symbolic Ring
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field'>
        sage: is_field(SR)
        True

        sage: F = FractionField(PolynomialRing(QQ,'t'))
        sage: t = F.gen()
        sage: E = EllipticCurve([t,0]); E
        Elliptic Curve defined by y^2 = x^3 + t*x over Fraction Field of Univariate Polynomial Ring in t over Rational Field
        sage: type(E)
        <class 'sage.schemes.elliptic_curves.ell_field.EllipticCurve_field'>


    """
    import ell_generic, ell_field, ell_finite_field, ell_number_field, ell_rational_field, ell_padic_field  # here to avoid circular includes
    
    if j is not None:
        if not x is None:
            if rings.is_Ring(x):
                try:
                    j = x(j)
                except (ZeroDivisionError, ValueError, TypeError):                    
                    raise ValueError, "First parameter must be a ring containing %s"%j
            else:
                raise ValueError, "First parameter (if present) must be a ring when j is specified"
        return EllipticCurve_from_j(j)

    assert x is not None
    
    if is_SymbolicEquation(x):
        x = x.lhs() - x.rhs()
    
    if parent(x) is SR:
        x = x._polynomial_(rings.QQ['x', 'y'])
    
    if rings.is_MPolynomial(x) and y is None:
        f = x
        if f.degree() != 3:
            raise ValueError, "Elliptic curves must be defined by a cubic polynomial."
        if f.degrees() == (3,2):
            x, y = f.parent().gens()
        elif f.degree() == (2,3):
            y, x = f.parent().gens()
        elif len(f.parent().gens()) == 2 or len(f.parent().gens()) == 3 and f.is_homogeneous():
            # We'd need a point too...
            raise NotImplementedError, "Construction of an elliptic curve from a generic cubic not yet implemented."
        else:
            raise ValueError, "Defining polynomial must be a cubic polynomial in two variables."

        try:
            if f.coefficient(x**3) < 0:
                f = -f
            # is there a nicer way to extract the coefficients?
            a1 = a2 = a3 = a4 = a6 = 0
            for coeff, mon in f:
                if mon == x**3:
                    assert coeff == 1
                elif mon == x**2:
                    a2 = coeff
                elif mon == x:
                    a4 = coeff
                elif mon == 1:
                    a6 = coeff
                elif mon == y**2:
                    assert coeff == -1
                elif mon == x*y:
                    a1 = -coeff
                elif mon == y:
                    a3 = -coeff
                else:
                    assert False
            return EllipticCurve([a1, a2, a3, a4, a6])
        except AssertionError:
            raise NotImplementedError, "Construction of an elliptic curve from a generic cubic not yet implemented."
    
    if rings.is_Ring(x):
        if rings.is_RationalField(x):
            return ell_rational_field.EllipticCurve_rational_field(x, y)
        elif rings.is_FiniteField(x) or (rings.is_IntegerModRing(x) and x.characteristic().is_prime()):
            return ell_finite_field.EllipticCurve_finite_field(x, y)
        elif rings.is_pAdicField(x):
            return ell_padic_field.EllipticCurve_padic_field(x, y)
        elif rings.is_NumberField(x):
            return ell_number_field.EllipticCurve_number_field(x, y)
        elif rings.is_Field(x):
            return ell_field.EllipticCurve_field(x, y)
        return ell_generic.EllipticCurve_generic(x, y)

    if isinstance(x, unicode):
        x = str(x)
        
    if isinstance(x, str):
        return ell_rational_field.EllipticCurve_rational_field(x)
        
    if rings.is_RingElement(x) and y is None:
        from sage.misc.misc import deprecation
        deprecation("'EllipticCurve(j)' is deprecated; use 'EllipticCurve_from_j(j)' or 'EllipticCurve(j=j)' instead.")
        # Fixed for all characteristics and cases by John Cremona
        j=x
        F=j.parent().fraction_field()
        char=F.characteristic()
        if char==2:
            if j==0:
                return EllipticCurve(F, [ 0, 0, 1, 0, 0 ])
            else:
                return EllipticCurve(F, [ 1, 0, 0, 0, 1/j ])
        if char==3:
            if j==0:
                return EllipticCurve(F, [ 0, 0, 0, 1, 0 ])
            else:
                return EllipticCurve(F, [ 0, j, 0, 0, -j**2 ])
        if j == 0:
            return EllipticCurve(F, [ 0, 0, 0, 0, 1 ])
        if j == 1728:
            return EllipticCurve(F, [ 0, 0, 0, 1, 0 ])
        k=j-1728
        return EllipticCurve(F, [0,0,0,-3*j*k, -2*j*k**2])

    if not isinstance(x,list):
        raise TypeError, "invalid input to EllipticCurve constructor"

    x = Sequence(x)
    if not (len(x) in [2,5]):
        raise ValueError, "sequence of coefficients must have length 2 or 5"
    R = x.universe()

    if isinstance(x[0], (rings.Rational, rings.Integer, int, long)):
        return ell_rational_field.EllipticCurve_rational_field(x, y)

    elif rings.is_NumberField(R):
        return ell_number_field.EllipticCurve_number_field(x, y)

    elif rings.is_pAdicField(R):
        return ell_padic_field.EllipticCurve_padic_field(x, y)
    
    elif rings.is_FiniteField(R) or (rings.is_IntegerModRing(R) and R.characteristic().is_prime()):
        return ell_finite_field.EllipticCurve_finite_field(x, y)

    elif rings.is_Field(R):
        return ell_field.EllipticCurve_field(x, y)

    return ell_generic.EllipticCurve_generic(x, y)