diff --git a/src/sage/schemes/elliptic_curves/ell_field.py b/src/sage/schemes/elliptic_curves/ell_field.py index 4f694e0f252..7e27efcb7ac 100755 --- a/src/sage/schemes/elliptic_curves/ell_field.py +++ b/src/sage/schemes/elliptic_curves/ell_field.py @@ -1529,6 +1529,55 @@ def isogeny_codomain(self, kernel): E._fetch_cached_order(self) return E + def period_lattice(self): + r""" + Return the period lattice of the elliptic curve for the given + embedding of its base field with respect to the differential + `dx/(2y + a_1x + a_3)`. + + Only supported for some base rings. + + EXAMPLES:: + + sage: EllipticCurve(RR, [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 6.00000000000000 over Real Field with 53 bits of precision + + TESTS:: + + sage: EllipticCurve(QQ, [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + x + 6 over Rational Field + sage: EllipticCurve(RR, [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 6.00000000000000 over Real Field with 53 bits of precision + sage: EllipticCurve(RealField(100), [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + 1.0000000000000000000000000000*x + 6.0000000000000000000000000000 over Real Field with 100 bits of precision + sage: EllipticCurve(CC, [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + 1.00000000000000*x + 6.00000000000000 over Complex Field with 53 bits of precision + sage: EllipticCurve(ComplexField(100), [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + 1.0000000000000000000000000000*x + 6.0000000000000000000000000000 over Complex Field with 100 bits of precision + sage: EllipticCurve(AA, [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + x + 6 over Algebraic Real Field + sage: EllipticCurve(QQbar, [1, 6]).period_lattice() + Period lattice associated to Elliptic Curve defined by y^2 = x^3 + x + 6 over Algebraic Field + + Unsupported cases (the exact error being raised may change in the future):: + + sage: EllipticCurve(ZZ, [1, 6]).period_lattice() + Traceback (most recent call last): + ... + AttributeError: 'EllipticCurve_generic_with_category' object has no attribute 'period_lattice' + sage: QQt. = QQ[] + sage: EllipticCurve(QQt.fraction_field(), [1, 6]).period_lattice() + Traceback (most recent call last): + ... + AttributeError: 'FractionField_1poly_field_with_category' object has no attribute ... + sage: EllipticCurve(GF(7), [1, 6]).period_lattice() + Traceback (most recent call last): + ... + IndexError: list index out of range + """ + from sage.schemes.elliptic_curves.period_lattice import PeriodLattice_ell + return PeriodLattice_ell(self) + def kernel_polynomial_from_point(self, P, *, algorithm=None): r""" Given a point `P` on this curve which generates a rational subgroup, diff --git a/src/sage/schemes/elliptic_curves/period_lattice.py b/src/sage/schemes/elliptic_curves/period_lattice.py index e6008a09279..02fa7ce62ca 100755 --- a/src/sage/schemes/elliptic_curves/period_lattice.py +++ b/src/sage/schemes/elliptic_curves/period_lattice.py @@ -111,11 +111,12 @@ from sage.misc.cachefunc import cached_method from sage.misc.lazy_import import lazy_import from sage.modules.free_module import FreeModule_generic_pid -from sage.rings.complex_mpfr import ComplexField, ComplexNumber +from sage.rings.complex_mpfr import ComplexField, ComplexNumber, ComplexField_class from sage.rings.infinity import Infinity from sage.rings.integer_ring import ZZ +from sage.rings.qqbar import AA, QQbar from sage.rings.rational_field import QQ -from sage.rings.real_mpfr import RealField, RealNumber +from sage.rings.real_mpfr import RealField, RealField_class, RealNumber from sage.schemes.elliptic_curves.constructor import EllipticCurve from sage.structure.richcmp import richcmp_method, richcmp, richcmp_not_equal @@ -212,9 +213,16 @@ def __init__(self, E, embedding=None): sage: L = PeriodLattice_ell(E,emb) sage: L == loads(dumps(L)) True - """ - from sage.rings.qqbar import AA, QQbar + Elliptic curve over imaginary number field without ``embedding`` specified:: + + sage: E = EllipticCurve(QQ[I], [5, -3*I]) + sage: L = PeriodLattice_ell(E, embedding=None) + sage: L.elliptic_logarithm(E(I+1, I+2)) + -0.773376784700140 - 0.177736018028666*I + sage: L.elliptic_exponential(_) + (1.00000000000000 - 1.00000000000000*I : 2.00000000000000 - 1.00000000000000*I : 1.00000000000000) + """ # First we cache the elliptic curve with this period lattice: self.E = E @@ -223,12 +231,20 @@ def __init__(self, E, embedding=None): # the given embedding: K = E.base_field() + self.is_approximate = isinstance(K, (RealField_class, ComplexField_class)) if embedding is None: - embs = K.embeddings(AA) - real = len(embs) > 0 - if not real: - embs = K.embeddings(QQbar) - embedding = embs[0] + if K in (AA, QQbar): + embedding = K.hom(QQbar) + real = K == AA + elif self.is_approximate: + embedding = K.hom(K) + real = isinstance(K, RealField_class) + else: + embs = K.embeddings(AA) + real = len(embs) > 0 + if not real: + embs = K.embeddings(QQbar) + embedding = embs[0] else: embedding = refine_embedding(embedding, Infinity) real = embedding(K.gen()).imag().is_zero() @@ -255,20 +271,24 @@ def __init__(self, E, embedding=None): # The ei are used both for period computation and elliptic # logarithms. - self.Ebar = self.E.change_ring(self.embedding) - self.f2 = self.Ebar.two_division_polynomial() + if self.is_approximate: + self.f2 = self.E.two_division_polynomial() + else: + self.Ebar = self.E.change_ring(self.embedding) + self.f2 = self.Ebar.two_division_polynomial() if self.real_flag == 1: # positive discriminant - self._ei = self.f2.roots(AA,multiplicities=False) + self._ei = self.f2.roots(K if self.is_approximate else AA,multiplicities=False) self._ei.sort() # e1 < e2 < e3 e1, e2, e3 = self._ei elif self.real_flag == -1: # negative discriminant - self._ei = self.f2.roots(QQbar, multiplicities=False) + self._ei = self.f2.roots(ComplexField(K.precision()) if self.is_approximate else QQbar, multiplicities=False) self._ei = sorted(self._ei, key=lambda z: z.imag()) e1, e3, e2 = self._ei # so e3 is real - e3 = AA(e3) + if not self.is_approximate: + e3 = AA(e3) self._ei = [e1, e2, e3] else: - self._ei = self.f2.roots(QQbar, multiplicities=False) + self._ei = self.f2.roots(ComplexField(K.precision()) if self.is_approximate else QQbar, multiplicities=False) e1, e2, e3 = self._ei # The quantities sqrt(e_i-e_j) are cached (as elements of @@ -329,7 +349,8 @@ def __repr__(self): To: Algebraic Real Field Defn: a |--> 1.259921049894873? """ - if self.E.base_field() is QQ: + K = self.E.base_field() + if K in (QQ, AA, QQbar) or isinstance(K, (RealField_class, ComplexField_class)): return "Period lattice associated to %s" % (self.E) return "Period lattice associated to %s with respect to the embedding %s" % (self.E, self.embedding) @@ -630,6 +651,13 @@ def tau(self, prec=None, algorithm='sage'): w1, w2 = self.normalised_basis(prec=prec, algorithm=algorithm) return w1/w2 + @cached_method + def _compute_default_prec(self): + r""" + Internal function to compute the default precision to be used if nothing is passed in. + """ + return self.E.base_field().precision() if self.is_approximate else RealField().precision() + @cached_method def _compute_periods_real(self, prec=None, algorithm='sage'): r""" @@ -670,13 +698,13 @@ def _compute_periods_real(self, prec=None, algorithm='sage'): 1.9072648860892725468182549468 - 1.3404778596244020196600112394*I) """ if prec is None: - prec = 53 + prec = self._compute_default_prec() R = RealField(prec) C = ComplexField(prec) if algorithm == 'pari': ainvs = self.E.a_invariants() - if self.E.base_field() is not QQ: + if self.E.base_field() is not QQ and not self.is_approximate: ainvs = [C(self.embedding(ai)).real() for ai in ainvs] # The precision for omega() is determined by ellinit() @@ -688,9 +716,8 @@ def _compute_periods_real(self, prec=None, algorithm='sage'): raise ValueError("invalid value of 'algorithm' parameter") pi = R.pi() - # Up to now everything has been exact in AA or QQbar, but now - # we must go transcendental. Only now is the desired - # precision used! + # Up to now everything has been exact in AA or QQbar (unless self.is_approximate), + # but now we must go transcendental. Only now is the desired precision used! if self.real_flag == 1: # positive discriminant a, b, c = (R(x) for x in self._abc) w1 = R(pi/a.agm(b)) # least real period @@ -758,12 +785,11 @@ def _compute_periods_complex(self, prec=None, normalise=True): 0.692321964451917 """ if prec is None: - prec = RealField().precision() + prec = self._compute_default_prec() C = ComplexField(prec) - # Up to now everything has been exact in AA, but now we - # must go transcendental. Only now is the desired - # precision used! + # Up to now everything has been exact in AA or QQbar (unless self.is_approximate), + # but now we must go transcendental. Only now is the desired precision used! pi = C.pi() a, b, c = (C(x) for x in self._abc) if (a+b).abs() < (a-b).abs(): @@ -1107,7 +1133,7 @@ def sigma(self, z, prec=None, flag=0): 2.60912163570108 - 0.200865080824587*I """ if prec is None: - prec = RealField().precision() + prec = self._compute_default_prec() try: return self.E.pari_curve().ellsigma(z, flag, precision=prec) except AttributeError: @@ -1421,7 +1447,7 @@ def e_log_RC(self, xP, yP, prec=None, reduce=True): 2.06711431204080 - 1.73451485683471*I """ if prec is None: - prec = RealField().precision() + prec = self._compute_default_prec() # Note: using log2(prec) + 3 guard bits is usually enough. # To avoid computing a logarithm, we use 40 guard bits which # should be largely enough in practice. @@ -1709,11 +1735,61 @@ def elliptic_logarithm(self, P, prec=None, reduce=True): 1.17058357737548897849026170185581196033579563441850967539191867385734983296504066660506637438866628981886518901958717288150400849746892393771983141354 - 1.13513899565966043682474529757126359416758251309237866586896869548539516543734207347695898664875799307727928332953834601460994992792519799260968053875*I sage: L.elliptic_logarithm(P, prec=1000) 1.17058357737548897849026170185581196033579563441850967539191867385734983296504066660506637438866628981886518901958717288150400849746892393771983141354014895386251320571643977497740116710952913769943240797618468987304985625823413440999754037939123032233879499904283600304184828809773650066658885672885 - 1.13513899565966043682474529757126359416758251309237866586896869548539516543734207347695898664875799307727928332953834601460994992792519799260968053875387282656993476491590607092182964878750169490985439873220720963653658829712494879003124071110818175013453207439440032582917366703476398880865439217473*I + + Elliptic curve over ``QQbar``:: + + sage: E = EllipticCurve(QQbar, [sqrt(2), I]) + sage: L = E.period_lattice() + sage: P = E.lift_x(3) + sage: L.elliptic_logarithm(P) + -1.97657221097437 - 1.05021415535949*I + sage: L.elliptic_exponential(_) + (3.00000000000000 + 9.20856947066460e-16*I : -5.59022723358798 - 0.0894418024719718*I : 1.00000000000000) + sage: L.elliptic_logarithm(P, prec=100) + -3.4730631218714889933426781799 + 0.44627675553762761312098773197*I + sage: L.elliptic_exponential(_) + (3.0000000000000000000000000000 - 1.4773628579202938936348512161e-30*I : -5.5902272335879800026836302686 - 0.089441802471969391005702381090*I : 1.0000000000000000000000000000) + + Real approximate field, negative discriminant. Note that the output precision uses the precision of the base field:: + + sage: E = EllipticCurve(RealField(100), [1, 6]) + sage: L = E.period_lattice() + sage: L.real_flag + -1 + sage: P = E(3, 6) + sage: L.elliptic_logarithm(P) + 2.4593388737550379526023682666 + sage: L.elliptic_exponential(_) + (3.0000000000000000000000000000 : 5.9999999999999999999999999999 : 1.0000000000000000000000000000) + + Real approximate field, positive discriminant:: + + sage: E = EllipticCurve(RealField(100), [-4, 3]) + sage: L = E.period_lattice() + sage: L.real_flag + 1 + sage: P = E.lift_x(4) + sage: L.elliptic_logarithm(P) + 0.51188849089267627141925354967 + sage: L.elliptic_exponential(_) + (4.0000000000000000000000000000 : -7.1414284285428499979993998114 : 1.0000000000000000000000000000) + + Complex approximate field:: + + sage: E = EllipticCurve(ComplexField(100), [I, 3*I+4]) + sage: L = E.period_lattice() + sage: L.real_flag + 0 + sage: P = E.lift_x(4) + sage: L.elliptic_logarithm(P) + -1.1447032790074574712147458157 - 0.72429843602171875396186134806*I + sage: L.elliptic_exponential(_) + (4.0000000000000000000000000000 + 1.2025589033682610849950210280e-30*I : -8.2570982991257407680322611854 - 0.42387771989714340809597881586*I : 1.0000000000000000000000000000) """ if P.curve() is not self.E: raise ValueError("Point is on the wrong curve") if prec is None: - prec = RealField().precision() + prec = self._compute_default_prec() if P.is_zero(): return ComplexField(prec)(0) @@ -1926,7 +2002,10 @@ def elliptic_exponential(self, z, to_curve=True): if to_curve: K = x.parent() - v = refine_embedding(self.embedding, Infinity) + if self.is_approximate: + v = self.embedding + else: + v = refine_embedding(self.embedding, Infinity) a1, a2, a3, a4, a6 = (K(v(a)) for a in self.E.ainvs()) b2 = K(v(self.E.b2())) x = x - b2 / 12