10.1.3.1 EllipticCurve_rational_field Objects

class EllipticCurve_rational_field
Elliptic curve over the Rational Field.
EllipticCurve_rational_field( ainvs, [extra=None])

Instances of class EllipticCurve_rational_field have the following methods (in addition to inherited methods and special methods):

an,$  $ analytic_rank,$  $ anlist,$  $ ap,$  $ aplist,$  $ complex_area,$  $ conductor,$  $ CPS_height_bound,$  $ cremona_label,$  $ database_curve,$  $ eval_modular_form,$  $ gens,$  $ has_cm,$  $ heegner_discriminants,$  $ heegner_discriminants_list,$  $ heegner_index,$  $ heegner_index_bound,$  $ heegner_point_height,$  $ is_integral,$  $ is_minimal,$  $ is_semistable,$  $ is_surjective,$  $ isogenous_curves,$  $ isogeny_class,$  $ kodaira_type,$  $ L1_vanishes,$  $ L_ratio,$  $ Lambda,$  $ Lseries,$  $ Lseries_at1,$  $ Lseries_deriv_at1,$  $ Lseries_extended,$  $ minimal_model,$  $ modular_degree,$  $ modular_parametrization,$  $ mwrank_curve,$  $ newform,$  $ ngens,$  $ non_surjective,$  $ Np,$  $ omega,$  $ p_isogenous_curves,$  $ pari_curve,$  $ pari_mincurve,$  $ period_lattice,$  $ point_search,$  $ quadratic_twist,$  $ rank,$  $ real_components,$  $ regulator,$  $ root_number,$  $ satisfies_heegner_hypothesis,$  $ saturation,$  $ sea,$  $ selmer_rank_bound,$  $ sha_an,$  $ shabound,$  $ shabound_kato,$  $ shabound_kolyvagin,$  $ sigma,$  $ silverman_height_bound,$  $ tamagawa_number,$  $ tamagawa_product,$  $ torsion_order,$  $ torsion_subgroup,$  $ two_descent,$  $ two_selmer_shabound,$  $ two_torsion_rank,$  $ watkins_data

Further documentation:

an( n)

The n-th Fourier coefficient of the modular form corresponding to this elliptic curve, where n is a positive integer.

analytic_rank( )

Return an approximation for the analytic rank of this elliptic curve.

The approximation is computed using the Buhler-Gross algorithm as implemented in GP by Tom Womack and John Cremona, who note that their implementation is practical for any rank and conductor $ \leq 10^{10}$ in 10 minutes.

(NOTE: Magma's analytic rank command, due to Mark Watkins, is significantly faster.)

anlist( n)

The Fourier coefficients up to and including a_n of the modular form attached to this elliptic curve. The ith element of the return list is a[i].

sage: E = EllipticCurve([0, -1, 1, -10, -20])
sage: E.anlist(3)
[0, 1, -2, -1]

sage: E = EllipticCurve([0,1])
sage: E.anlist(20)
[0, 1, 0, 0, 0, 0, 0, -4, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 8, 0]

ap( p)

The p-th Fourier coefficient of the modular form corresponding to this elliptic curve, where p is prime.

aplist( pmax)

Return list of pairs (p, a_p(E)) for p up to pmax.

complex_area( )

Return the area of a fundamental domain for the period lattice of the elliptic curve.

conductor( [algorithm=pari])

Returns the conductor of the elliptic curve.

INPUT:
    algorithm -- str, (default: "pari")
           "pari"   -- use the PARI C-library ellglobalred
                       implementation of Tate's algorithm
           "mwrank" -- use Cremona's mwrank implementation of
                       Tate's algorithm; can be faster if the
                       curve has integer coefficients (TODO:
                       limited to small conductor until mwrank
                       gets integer factorization)
           "all" -- use both implementations, verify that the
                    results are the same (or raise an error),
                    and output the common value.

sage: E = EllipticCurve([1, -1, 1, -29372, -1932937])
sage: E.conductor(algorithm="pari")
3006
sage: E.conductor(algorithm="mwrank")
3006
sage: E.conductor(algorithm="all")
3006

NOTE: The conductor computed using each algorithm is cached separately. Thus calling E.conductor("pari"), then E.conductor("mwrank") and getting the same result checks that both systems compute the same answer.

CPS_height_bound( )

Return the Cremona-Prickett-Siksek height bound. This is a floating point number B such that if P is a point on the curve, then the naive logarithmetic height of P is off from the canonical height by at most B.

sage: E = EllipticCurve("11a")
sage: E.CPS_height_bound()
2.8774743273580445
sage: E = EllipticCurve("5077a")
sage: E.CPS_height_bound()
0.0
sage: E = EllipticCurve([1,2,3,4,1])
sage: E.CPS_height_bound()
Traceback (most recent call last):
...
RuntimeError: curve must be minimal.
sage: F = E.quadratic_twist(-19)
sage: F
Elliptic Curve defined by y^2 + x*y + y = x^3 - x^2 + 1376*x - 130 over
Rational Field
sage: F.CPS_height_bound()
0.65551583769728516

IMPLEMENTATION: Call the corresponding mwrank C++ library function.

cremona_label( [space=False])

Return the Cremona label associated to (the minimal model) of this curve, if it is known. If not, raise a RuntimeError exception.

database_curve( )

Return the curve in the elliptic curve database isomorphic to this curve, if possible. Otherwise raise a RuntimeError exception.

The following examples assumes that the elliptic curve database is installed.

sage: E = EllipticCurve([0,1,2,3,4])
sage: E.database_curve()
Elliptic Curve defined by y^2  = x^3 + x^2 + 3*x + 5 over Rational Field

NOTES: The model of the curve in the database can be different than the Weierstrass model for this curve, since database models are always minimal.

gens( [verbose=False], [rank1_search=10], [only_use_mwrank=False])

Compute and return generators for the Mordell-Weil group E(Q) *modulo* torsion.

TODO: Right now this function assumes that the input curve to be in minimal Weierstrass form. This restriction will be removed in the near future.

INPUT:
    verbose -- (default: None), if specified changes the
               verbosity of mwrank computations.
    rank1_search -- (default: 16), if the curve has analytic
               rank 1, try to find a generator by a direct
               search up to this logarithmic height.  If this
               fails the usual mwrank procedure is called.
OUTPUT:
    generators -- List of generators for the Mordell-Weil group.

IMPLEMENTATION: Uses Cremona's mwrank C library.

heegner_discriminants_list( n)

List of the first n Heegner discriminants for self.

heegner_index( D, [min_p=False], [prec=5], [verbose=3])

Returns the index of the Heegner point on the quadratic twist by D of the rank ZERO curve self.

Return (an interval that contains) the square of the odd part of the index of the Heegner point in the group of K-rational points *modulo torsion* on the twist of the elliptic curve by D.

If 0 is in the interval of the height of the Heegner point computed to the given prec, then this function returns 0.

INPUT:
    D (int) -- Heegner discriminant
    min_p (int) -- (default: 3) only rule out primes >= min_p
                   dividing the index.  
    verbose (bool) -- (default: False); print lots of mwrank search status
                                        information when computing
regulator
    prec (int) -- (default: 5), use prec*sqrt(N) + 20 terms
                  of L-series in computations, where N is the
                  conductor.
OUTPUT:
    an interval that contains the index

sage: E = EllipticCurve('11a')
sage: E.heegner_discriminants(50)
[-7, -8, -19, -24, -35, -39, -40, -43]
sage: E.heegner_index(-7)
[0.999993856229,1.00000616632]

sage: E = EllipticCurve('37b')
sage: E.heegner_discriminants(100)
[-3, -4, -7, -11, -40, -47, -67, -71, -83, -84, -95]
sage: E.heegner_index(-95)
[3.99999236227,4.00000791569]

Current discriminants -3 and -4 are not supported:

sage: E.heegner_index(-3)
Traceback (most recent call last):
...
ArithmeticError: Discriminant (=-3) must not be -3 or -4.

heegner_index_bound( [D=21], [prec=True], [verbose=5], [max_height=0])

Assume self has rank 0.

Return a list v of primes such that if an odd prime p divides the index of the the Heegner point in the group of rational points *modulo torsion*, then p is in v.

If 0 is in the interval of the height of the Heegner point computed to the given prec, then this function returns v = 0. This does not mean that the Heegner point is torsion, just that it is very likely torsion.

If we obtain no information from a search up to max_height, e.g., if the Siksek et al. bound is bigger than max_height, then we return v = -1.

INPUT:
    D (int) -- (deault: 0) Heegner discriminant; if 0, use the
               first discriminant < -4 that satisfies the Heegner
hypothesis
    verbose (bool) -- (default: True)
    prec (int) -- (default: 5), use prec*sqrt(N) + 20 terms
                  of L-series in computations, where N is the
                  conductor.
    max_height (float) -- should be <= 21; bound on logarithmic naive
height
                          used in point searches.  Make smaller to make
this
                          function faster, at the expense of possibly
obtaining
                          a worse answer.  A good range is between 13 and
21.
                          
OUTPUT:
    v -- list or int (bad primes or 0 or -1)
    D -- the discriminant that was used (this is useful if D was
         automatically selected).

heegner_point_height( D, [prec=2])

Use the Gross-Zagier formula to compute the Neron-Tate canonical height over K of the Heegner point corresponding to D, as an Interval (since it's computed to some precision using L-functions).

INPUT:
    D (int) -- fundamental discriminant (=/= -3, -4)
    prec (int) -- (default: 2), use prec*sqrt(N) + 20 terms
                  of L-series in computations, where N is the
                  conductor.

OUTPUT:
    Interval that contains the height of the Heegner point.

sage: E = EllipticCurve('11a')
sage: E.heegner_point_height(-7)
[0.222270926217,0.222273662409]

is_surjective( p, [A=1000])

Return True if the mod-p representation attached to E is surjective, False if it is not, or None if we were unable to determine whether it is or not.

INPUT:
    p -- int (a prime number)
    A -- int (a bound on the number of a_p to use)

OUTPUT:
    a 2-tuple:
    -- surjective or (probably) not
    -- information about what it is if not surjective

REMARKS:

1. If p >= 5 then the mod-p representation is surjective if and only if the p-adic representation is surjective. When p = 2, 3 there are counterexamples. See a very recent paper of Elkies for more details when p=3.

2. When p <= 3 this function always gives the correct result irregardless of A, since it explicitly determines the p-division polynomial.

isogenous_curves( )

Return a list of pairs $ (p, L)$ where $ p$ is a prime and $ L$ is a list of the elliptic curves over $ \mathbf{Q}$ that are $ p$ -isogenous to this elliptic curve.

This is implemented using Cremona's GP script allisog.gp.

sage: E = EllipticCurve([0,-1,0,-24649,1355209])
sage: E.isogenous_curves()
[(2, [Elliptic Curve defined by y^2  = x^3 - x^2 - 91809*x - 9215775 over
Rational Field, Elliptic Curve defined by y^2  = x^3 - x^2 - 383809*x +
91648033 over Rational Field, Elliptic Curve defined by y^2  = x^3 - x^2 +
1996*x + 102894 over Rational Field])]

isogeny_class( )

Return all curves over $ \mathbf{Q}$ in the isogeny class of this elliptic curve.

sage: E = EllipticCurve([0,-1,0,-24649,1355209])
sage: E.isogeny_class()
[Elliptic Curve defined by y^2  = x^3 - x^2 - 24649*x + 1355209 over
Rational Field, Elliptic Curve defined by y^2  = x^3 - x^2 - 91809*x -
9215775 over Rational Field, Elliptic Curve defined by y^2  = x^3 - x^2 -
383809*x + 91648033 over Rational Field, Elliptic Curve defined by y^2  =
x^3 - x^2 + 1996*x + 102894 over Rational Field]

kodaira_type( p)

Local Kodaira type of the elliptic curve at p.

1 means good reduction (type $ I_0$ ), 2, 3 and 4 mean types II, III and IV, respectively, $ 4 + \nu$ with $ \nu > 0$ means type $ I_{\nu}$ ; finally the opposite values -1, -2, etc. refer to the starred types $ I_0^*$ , $ II^*$ , etc.

L1_vanishes( )

Returns whether or not L(E,1) = 0. The result is provably correct if the Manin constant of the associated optimal quotient is <= 2. This hypothesis on the Manin constant is true for all curves of conductor <= 40000 (by Cremona) and all semistable curves (i.e., squarefree conductor).

sage: E = EllipticCurve([0, -1, 1, -10, -20])   # 11A  = X_0(11)
sage: E.L1_vanishes()
False
sage: E = EllipticCurve([0, -1, 1, 0, 0])       # X_1(11)
sage: E.L1_vanishes()
False
sage: E = EllipticCurve([0, 0, 1, -1, 0])       # 37A  (rank 1)
sage: E.L1_vanishes()
True
sage: E = EllipticCurve([0, 1, 1, -2, 0])       # 389A (rank 2)
sage: E.L1_vanishes()
True
sage: E = EllipticCurve([0, 0, 1, -38, 90])     # 361A (CM curve))
sage: E.L1_vanishes()
True
sage: E = EllipticCurve([0,-1,1,-2,-1])         # 141C (13-isogeny)
sage: E.L1_vanishes()
False

WARNING: It's conceivable that machine floats are not large enough precision for the computation; if this could be the case a RuntimeError is raised. The curve's real period would have to be very small for this to occur.

ALGORITHM: Compute the root number. If it is -1 then L(E,s) vanishes to odd order at 1, hence vanishes. If it is +1, use a result about modular symbols and Mazur's "Rational Isogenies" paper to determine a provably correct bound (assuming Manin constant is <= 2) so that we can determine whether L(E,1) = 0.

AUTHOR: William Stein, 2005-04-20.

L_ratio( )

Returns the ratio L(E,1)/Omega as an exact rational number. The result is *provably* correct if the Manin constant of the associated optimal quotient is <= 2. This hypothesis on the Manin constant is true for all semistable curves (i.e., squarefree conductor), by a theorem of Mazur from his "Rational Isogenies of Prime Degree" paper.

sage: E = EllipticCurve([0, -1, 1, -10, -20])   # 11A  = X_0(11)
sage: E.L_ratio()
1/5
sage: E = EllipticCurve([0, -1, 1, 0, 0])       # X_1(11)
sage: E.L_ratio()
1/25
sage: E = EllipticCurve([0, 0, 1, -1, 0])       # 37A  (rank 1)
sage: E.L_ratio()
0
sage: E = EllipticCurve([0, 1, 1, -2, 0])       # 389A (rank 2)
sage: E.L_ratio()
0
sage: E = EllipticCurve([0, 0, 1, -38, 90])     # 361A (CM curve))
sage: E.L_ratio()
0
sage: E = EllipticCurve([0,-1,1,-2,-1])         # 141C (13-isogeny)
sage: E.L_ratio()
1

WARNING: It's conceivable that machine floats are not large enough precision for the computation; if this could be the case a RuntimeError is raised. The curve's real period would have to be very small for this to occur.

ALGORITHM: Compute the root number. If it is -1 then L(E,s) vanishes to odd order at 1, hence vanishes. If it is +1, use a result about modular symbols and Mazur's "Rational Isogenies" paper to determine a provably correct bound (assuming Manin constant is <= 2) so that we can determine whether L(E,1) = 0.

AUTHOR: William Stein, 2005-04-20.

Lambda( s, prec)

Returns the value of the Lambda-series of the elliptic curve E at s can be any complex number. Use Lambda(s) if s is real, since it will be much faster.

Warning: This function uses sage.functions.transcendental.gamma_inc, which currently calls mathematica.

Lseries( s)

Returns the value of the L-series of the elliptic curve E at s, where s must be a real number.

NOTES: (1) If the conductor of the curve is large, say > $ 10^12$ , then this function will take a long time, since it uses an O(sqrt(N)) algorithm.

(2) There is an algorithm to compute L(E,s) for any complex s, but it involves computing the incomplete Gamma function, which is not implemented in SAGE.

sage: E = EllipticCurve([1,2,3,4,5])

sage: E.Lseries(1)
0.000000

(The following may have low order bits that are different on a 64-bit machine.)

sage: E.Lseries(1.1)    
0.285491007678148128442883

Lseries_at1( [k=0])

Compute $ L(E,1)$ using $ k$ terms of the series for $ L(E,1)$ as explained on page 406 of Henri Cohen's book"A Course in Computational Algebraic Number Theory". If the argument $ k$ is not specified, then it defaults to $ \sqrt(N)$ , where $ N$ is the conductor.

The real precision used in each step of the computation is the precision of machine floats.

INPUT:
    k -- (optional) an integer, defaults to sqrt(N).
    
OUTPUT:
    float -- L(E,1)
    float -- a bound on the error in the approximation; this
             is a proveably correct upper bound on the sum
             of the tail end of the series used to compute L(E,1).

This function is disjoint from the PARI elllseries command, which is for a similar purpose. To use that command (via the PARI C library), simply type E.pari_mincurve().elllseries(1)

ALGORITHM:

  1. Compute the root number eps. If it is -1, return 0.

  2. Compute the Fourier coefficients a_n, for n up to and including k.

  3. Compute the sum

    $\displaystyle 2 * sum_{n=1}^{k} (a_n / n) * exp(-2*pi*n/Sqrt(N)),
$

    where N is the conductor of E.

  4. Compute a bound on the tail end of the series, which is

    $\displaystyle 2 * e^(-2 * pi * (k+1) / sqrt(N)) / (1 - e^(-2*pi/sqrt(N))).
$

    For a proof see [Grigov-Jorza-Patrascu-Patrikis-Stein].

Lseries_deriv_at1( [k=0])

Compute $ L'(E,1)$ using$ k$ terms of the series for $ L'(E,1)$ .

The algorithm used is from page 406 of Henri Cohen's book ``A Course in Computational Algebraic Number Theory.''

The real precision of the computation is the precision of Python floats.

INPUT:
    k -- int; number of terms of the series

OUTPUT:
    real number -- an approximation for L'(E,1)
    real number -- a bound on the error in the approximation

ALGORITHM: 1. Compute the root number eps. If it is 1, return 0.

2. Compute the Fourier coefficients a_n, for n up to and including k.

3. Compute the sum

$\displaystyle 2 * sum_{n=1}^{k} (a_n / n) * E_1(2*pi*n/Sqrt(N)),
$

where N is the conductor of E, and E_1 is the exponential integral function.

4. Compute a bound on the tail end of the series, which is

$\displaystyle 2 * e^(-2 * pi * (k+1) / sqrt(N)) / (1 - e^(-2*pi/sqrt(N))).
$

For a proof see [Grigov-Jorza-Patrascu-Patrikis-Stein]. This is exactly the same as the bound for the approximation to $ L(E,1)$ produced by Lseries_at1.

Lseries_extended( s, prec)

Returns the value of the L-series of the elliptic curve E at s can be any complex number using prec terms of the power series expansion.

Warning: This function uses sage.functions.transcendental.gamma_inc, which currently calls mathematica.

minimal_model( )

Return the unique minimal Weierstrass equation for this elliptic curve. This is the model with minimal discriminant and $ a_1,a_2,a_3 \in \{0,\pm 1\}$ .

modular_degree( )

Return the modular degree of this elliptic curve, computing using Mark Watkins's C implementation of his analytic symmetric square L-function algorithm.

The correctness of this function is subject to the following three hypothesis:

NOTE: Mark has a much more robust implementation available in MAGMA.

modular_parametrization( )

Computes and returns ...

newform( )

Returns the newform attached to this elliptic curve.

non_surjective( [A=1000])

Returns a list of primes p such that the mod-p representation rho_E,p *might* not be surjective (this list usually contains 2, because of shortcomings of the algorithm). If p is not in the returned list, then rho_E,p is provably surjective (see A. Cojocaru's paper). If the curve has CM then infinitely many representations are not surjective, so we simply return the sequence [(0,"cm")] and do no further computation.

INPUT:
    A -- an integer
OUTPUT:
    list -- if curve has CM, returns [(0,"cm")].  Otherwise, returns a
            list of primes where mod-p representation very likely
            not surjective.   At any prime not in this list,
            the representation is definitely surjective.

sage: E = EllipticCurve([0, 0, 1, -38, 90])  # 361A
sage: E.non_surjective()   # CM curve
[(0, 'cm')]

sage: E = EllipticCurve([0, -1, 1, 0, 0]) # X_1(11)
sage: E.non_surjective()
[(5, '5-torsion')]

sage: E = EllipticCurve([0, 0, 1, -1, 0]) # 37A
sage: E.non_surjective()
[]

sage: E = EllipticCurve([0,-1,1,-2,-1])   # 141C
sage: E.non_surjective()
[(13, [1])]

ALGORITHM: When p<=3 use division polynomials. For 5 <= p <= B, where B is Cojocaru's bound, use the results in Section 2 of Serre's inventiones paper"Sur Les Representations Modulaires Deg Degre 2 de Galqbar Over Q."

Np( p)

The number of points on E modulo p, where p is a prime of good reduction.

sage: E = EllipticCurve([0, -1, 1, -10, -20])
sage: E.Np(2)
5
sage: E.Np(3)
5
sage: E.conductor()
11
sage: E.Np(11)
Traceback (most recent call last):
...
ArithmeticError: p (=11) must be a prime of good reduction

omega( )

Returns the real period. This is the correct period in the BSD conjecture, i.e., it is the least real period * 2 when the period lattice is rectangular.

p_isogenous_curves( p)

Returns a list of the elliptic curves over $ \mathbf{Q}$ that are $ p$ -isogenous to this elliptic curve.

This is implemented using Cremona's GP script allisog.gp.

sage: E = EllipticCurve([0,-1,0,-24649,1355209])
sage: E.p_isogenous_curves(2)
[Elliptic Curve defined by y^2  = x^3 - x^2 - 91809*x - 9215775 over
Rational Field, Elliptic Curve defined by y^2  = x^3 - x^2 - 383809*x +
91648033 over Rational Field, Elliptic Curve defined by y^2  = x^3 - x^2 +
1996*x + 102894 over Rational Field]

pari_curve( )

Return the PARI curve corresponding to this elliptic curve.

sage: E = EllipticCurve([0, 0,1,-1,0])
sage: e = E.pari_curve()
sage: type(e)
<type 'gen.gen'>
sage: e.type()
't_VEC'
sage: e.ellan(10)
[1, -2, -3, 2, -2, 6, -1, 0, 6, 4]

sage: E = EllipticCurve(RationalField(), ['1/3', '2/3'])
sage: e = E.pari_curve()
sage: e.type()
't_VEC'
sage: e[:5]
[0, 0, 0, 1/3, 2/3]

pari_mincurve( )

Return the PARI curve corresponding to a minimal model for this elliptic curve.

sage: E = EllipticCurve(RationalField(), ['1/3', '2/3'])
sage: e = E.pari_mincurve()
sage: e[:5]
[0, 0, 0, 27, 486]
sage: E.conductor()
47232
sage: e.ellglobalred()
[47232, [1, 0, 0, 0], 2]

period_lattice( )

Return a basis for the period lattice of the elliptic curve over Q as a 2-tuple.

The basis has the form [omega_1, omega_2], where Im(omega_1/omega_2) > 0 and omega_1 is real.

INPUT:
    -- an elliptic curve
OUTPUT:
    omega_1 -- complex number
    omega_2 -- complex number

point_search( height_limit, [verbose=True])

Search for points on a curve up to an input bound on the naive logarithmic height.

INPUT:
    height_limit (float) -- bound on naive height (at most 21, or mwrank
overflows)
    verbose  (bool) -- (default: True)

OUTPUT:
    points (list) -- list of points found

IMPLEMENTATION: Uses Cremona's mwrank package.

quadratic_twist( D)

Return the global minimal model of the quadratic twist of this curve by D.

rank( [use_database=False], [verbose=False])

Return the rank of this elliptic curve, assuming no conjectures.

If we fail to provably compute the rank, raises a RuntimeError exception.

INPUT:
    use_database (bool) -- (default: False), if True, try to
          look up the regulator in the Cremona database.
    proof (bool) -- (default: True), if True then rank is
          proven correct; otherwise, computation of rank is not certain.
    verbose -- (default: None), if specified changes the
               verbosity of mwrank computations.
    
OUTPUT:
    rank (int) -- the rank of the elliptic curve.

IMPLEMENTATION: Uses L-functions and mwrank.

real_components( )

Returns 1 if there is 1 real component and 2 if there are 2.

regulator( [use_database=None], [verbose=False])

Returns the regulator of this curve, which must be defined over Q.

INPUT:
    use_database -- bool (default: False), if True, try to
          look up the regulator in the Cremona database.
    verbose -- (default: None), if specified changes the
          verbosity of mwrank computations.

sage: E = EllipticCurve([0, 0, 1, -1, 0])
sage: E.regulator()
0.051111407578000000

root_number( )

Returns the root number of this elliptic curve.

This is 1 if the order of vanishing of the L-function L(E,s) at 1 is even, and -1 if it is odd.

satisfies_heegner_hypothesis( D)

Returns True precisely when D is a fundamental discriminant that satisfies the Heegner hypothesis for this elliptic curve.

saturation( points, [verbose=False], [max_prime=0], [odd_primes_only=False])

Given a list of rational points on E, compute the saturation in E(Q) of the subgroup they generate.

INPUT:
    points (list) -- list of points on E
    verbose  (bool) -- (default: False), if True, give verbose output
    max_prime (int) -- (default: 0), saturation is performed
                       for all primes up to max_prime.  If max_prime==0,
                       perform saturation at *all* primes, i.e., compute
                       the true saturation.
    odd_primes_only (bool) -- only do saturation at odd primes

OUTPUT:
    saturation (list) -- points that form a basis for the saturation
    index (int) -- the index of the group generated by points in their
saturation
    regulator (float) -- regulator of saturated points.

IMPLEMENTATION: Uses Cremona's mwrank package. With max_prime=0, we call mwrank with successively larger prime bounds until the full saturation is provably found. The results of saturation at the previous primes is stored in each case, so this should be reasonably fast.

sea( p, [early_abort=False])

Return the number of points on $ E$ over $ \mathbf{F}_p$ computed using the SEA algorithm, as implemented in PARI by Christophe Doche and Sylvain Duquesne.

INPUT:
    p -- a prime number
    early_abort -- bool (default: Falst); if True an early abort technique
               is used and the computation is interrupted as soon
               as a small divisor of the order is detected.

selmer_rank_bound( )

Bound on the rank of the curve, computed using the 2-selmer group. This is the rank of the curve minus the rank of the 2-torsion, minus a number determined by whatever mwrank was able to determine related to Sha[2]. Thus in many cases, this is the actual rank of the curve.

The following is the curve 960D1, which has rank 0, but Sha of order 4.

sage: E = EllipticCurve([0, -1, 0, -900, -10098])
sage: E.selmer_rank_bound()
0

It gives 0 instead of 2, because it knows Sha is nontrivial. In contrast, for the curve 571A, also with rank 0 and Sha of order 4, we get a worse bound:

sage: E = EllipticCurve([0, -1, 1, -929, -10595])
sage: E.selmer_rank_bound()
2
sage: E.rank()
0

sha_an( [use_database=False])

Returns the Birch and Swinnerton-Dyer conjectural order of Sha, unless the analytic rank is > 1, in which case this function returns 0.

This result is proved correct if the order of vanishing is 0 and the Manin constant is <= 2.

If the optional parameter use_database is True (default: False), this function returns the analytic order of Sha as listed in Cremona's tables, if this curve appears in Cremona's tables.

sage: E = EllipticCurve([0, -1, 1, -10, -20])   # 11A  = X_0(11)
sage: E.sha_an()
1
sage: E = EllipticCurve([0, -1, 1, 0, 0])       # X_1(11)
sage: E.sha_an()
1

The smallest conductor curve with nontrivial Sha:

sage: E = EllipticCurve([1,1,1,-352,-2689])     # 66B3
sage: E.sha_an()
4

The four optimal quotients with nontrivial Sha and conductor <= 1000:

sage: E = EllipticCurve([0, -1, 1, -929, -10595])       # 571A
sage: E.sha_an()
4
sage: E = EllipticCurve([1, 1, 0, -1154, -15345])       # 681B
sage: E.sha_an()
9
sage: E = EllipticCurve([0, -1, 0, -900, -10098])       # 960D
sage: E.sha_an()
4
sage: E = EllipticCurve([0, 1, 0, -20, -42])            # 960N
sage: E.sha_an()
4

The smallest conductor curve of rank > 1:

sage: E = EllipticCurve([0, 1, 1, -2, 0])       # 389A (rank 2)
sage: E.sha_an()
0

The following are examples that require computation of the Mordell-Weil group and regulator:

sage: E = EllipticCurve([0, 0, 1, -1, 0])                     # 37A  (rank 1)
sage: E.sha_an()
1

sage: E = EllipticCurve("1610f3")
sage: E.sha_an()
4

sage: e = EllipticCurve([1, 0, 0, -19491080, -33122512122])   # 15834T2
sage: e.sha_an()   # takes about 22 seconds
25

shabound( )

Compute a provably correct bound on the order of the Shafarevich-Tate group of this curve. The bound is a either False (no bound) or a list B of primes such that any divisor of Sha is in this list.

shabound_kato( )

Returns a list p of primes such tha theorems of Kato's and others (e.g., as explained in a paper/thesis of Grigor Grigorov) imply that if p divides $ \char93 Sha(E)$ then $ p$ is in the list.

If L(E,1) = 0, then Kato's theorem gives no information, so this function returns False.

THEOREM (Kato): Suppose p >= 5 is a prime so the p-adic representation rho_E,p is surjective. Then $ ord_p(\char93 Sha(E))$ divides $ ord_p(L(E,1)/Omega_E)$ .

sage: E = EllipticCurve([0, -1, 1, -10, -20])   # 11A  = X_0(11)
sage: E.shabound_kato()
[2, 3, 5]
sage: E = EllipticCurve([0, -1, 1, 0, 0])       # X_1(11)
sage: E.shabound_kato()
[2, 3, 5]
sage: E = EllipticCurve([1,1,1,-352,-2689])     # 66B3
sage: E.shabound_kato()
[2, 3]

For the following curve one really has 25 | $ \char93 Sha$ (by Grigorov-Stein paper):

sage: E = EllipticCurve([1, -1, 0, -332311, -73733731])   # 1058D1
sage: E.shabound_kato()
[2, 3, 5]
sage: E.non_surjective()
[]

For this one, Sha is divisible by 7.

sage: E = EllipticCurve([0, 0, 0, -4062871, -3152083138])   # 3364C1
sage: E.shabound_kato()
[2, 3, 7]

No information about curves of rank > 0:

sage: E = EllipticCurve([0, 0, 1, -1, 0])       # 37A  (rank 1)
sage: E.shabound_kato()
False

shabound_kolyvagin( [D=False], [regulator=None], [ignore_nonsurj_hypothesis=0])

Given a fundamental discriminant D (=-3,-4) that satisfies the Heegner hypothesis, return a list of primes so that Kolyvagin's theorem (as in Gross's paper) implies that any prime divisor of $ \char93 Sha$ is in this list.

INPUT:
    D -- (optional) a fundamental discriminant < -4 that satisfies the
         Heegner hypothesis for E; if not given, use the first such D
         
    regulator -- (optional) regulator of E(K); if not given, will
                 be computed (which could take a long time)

                 
    ignore_nonsurj_hypothesis (optional: default False) --
              If True, then gives the bound coming from Heegner point
              index, but without any hypothesis on surjectivity
              of the mod-p representation.
              

OUTPUT:
    bound and index

More precisely:

0 - if E/K has complex multiplication or analytic rank >= 2 or B - list of primes such that if p divides Sha(E/K), then p is in B.

and

I - the odd part of the index of the Heegner point in the full group of K-rational points on E. (If E has CM, returns 0.)

REMARKS: (1) We do not have to assume that the Manin constant is 1 (or a power of 2). If the Manin constant were divisible by a prime, that prime would get included in the list of bad primes.

(2) We assume the Gross-Zagier theorem is True under the hypothesis that gcd(N,D) = 1, instead of the stronger hypothesis gcd(2*N,D)=1 that is in the original Gross-Zagier paper. That Gross-Zagier is true when gcd(N,D)=1 is"well-known" to the experts, but doesn't seem to written up well in the literature.

(3) Correctness of the computation is guaranteed using interval arithmetic, under the assumption that the regulator, square root, and period lattice are computed to precision at least $ 10^{-10}$ , i.e., they are correct up to addition or a real number with absolute value less than $ 10^{-10}$ .

sigma( z, [flag=0])

Returns the value of the Weierstrass sigma function of the lattice associated to this elliptic curve E.

INPUT:
    z -- a complex number
    flag -- 0 - default ???
            1 - computes an arbitrary determination of log(sigma(z))
            2, 3 - same using the product expansion instead of theta
series.
                   ???
OUTPUT:
    a complex number

NOTE: The reason for the ???'s above, is that the PARI documentation for ellsigma is very vague.

silverman_height_bound( )

Return the Silverman height bound. This is a floating point number B such that if P is a point on the curve, then the naive logarithmetic height of P is off from the canonical height by at most B.

Note that the CPS_height_bound is typically much better than the Silverman bound.

tamagawa_number( p)

The Tamagawa number of the elliptic curve at $ p$ .

tamagawa_product( )

Returns the product of the Tamagawa numbers.

torsion_order( )

Return the order of the torsion subgroup.

torsion_subgroup( [flag=0])

Returns the torsion subgroup of this elliptic curve.

The flag is passed onto PARI and has the same algorithm meaning as there. So: If flag = 0, use Doud's algorithm; if flag = 1, use Lutz-Nagell.

two_descent( [verbose=1], [selmer_only=-1], [first_limit=8], [second_limit=20], [n_aux=False], [second_descent=True])

Compute 2-descent data for this curve.

INPUT:
    verbose     -- (default: True) print what mwrank is doing
    selmer_only -- (default: False) selmer_only switch
    first_limit -- (default: 20) firstlim is bound on |x|+|z|
    second_limit-- (default: 8)  secondlim is bound on log max {|x|,|z| },
                                 i.e. logarithmic
    n_aux       -- (default: -1) n_aux only relevant for general
                   2-descent when 2-torsion trivial; n_aux=-1 causes
default
                   to be used (depends on method)
    second_descent -- (default: True) second_descent only relevant for
                   descent via 2-isogeny
OUTPUT:
    Nothing -- nothing is returned (though much is printed)

two_selmer_shabound( )

Returns a bound on the dimension of Sha(E)[2], computed using a 2-descent.

watkins_data( )

Return a dict of the data computed by Mark Watkins's ec program applied to this elliptic curve.

Instances of class EllipticCurve_rational_field also have the following special methods:

_EllipticCurve_rational_field__pari_double_prec,$  $ _set_conductor,$  $ _set_cremona_label,$  $ _set_gens,$  $ _set_modular_degree,$  $ _set_rank,$  $ _set_torsion_order,$  $ _type

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