It's fixed (patch posted to trac). As suspected, it was a bug introduced in
the ell_rational_field refactoring.
David
On Nov 21, 2007 12:25 PM, William Stein <[EMAIL PROTECTED]> wrote:
>
> On Nov 20, 2007 1:40 PM, Paul Zimmermann <[EMAIL PROTECTED]> wrote:
> > William,
> >
> > sage told me to report you, thus I do:
> [... see below]
>
> For the particular curve you're considering mwrank (via sage's rank
> command)
> can compute the rank -- which is what you want -- in 0.5 seconds, so maybe
> you can use .rank() instead?
>
> {{{id=24|
> e = EllipticCurve([0, 33076156654533652066609946884, 0,
> 347897536144342179642120321790729023127716119338758604800,
> 114112815436927429551902303280680424778815462104985764887003237028585178\
> 1352816640000])
> }}}
>
> {{{id=27|
> time e.rank()
> ///
> 1
> CPU time: 0.00 s, Wall time: 0.46 s
> }}}
>
> That said, the fact that e.torsion_order() fails is certainly a bug:
>
> {{{id=29|
> e.torsion_order()
> ///
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "/Users/was/sage_notebook/worksheets/admin/23/code/91.py", line
> 4, in <module>
> ...
> self.__torsion_subgroup =
> rational_torsion.EllipticCurveTorsionSubgroup(self, flag)
> File
> "/Users/was/s/local/lib/python2.5/site-packages/sage/schemes/elliptic_curves/rational_torsion.py",
> line 56, in __init__
> self.__E.__pari_double_prec()
> AttributeError: 'EllipticCurve_rational_field' object has no attribute
> '_EllipticCurveTorsionSubgroup__pari_double_prec'
> }}}
>
> This is now trac #1237
> http://trac.sagemath.org/sage_trac/ticket/1237
> and it probably won't be too hard to fix. I suspect it was caused perhaps
> by David Roe's recent refactoring of the code for elliptic curve over QQ,
> but I couldn't be completely wrong.
>
>
> > sage: d = 919681/88529281
> > sage: _ = magma.eval('K := Rationals()')
> > sage: _ = magma.eval('P<x,y,z>:=ProjectiveSpace(K,2)')
> > sage: def rank(d):
> > ....: s='f := (x^2+y^2)*z^2-z^4-('
> > ....: s=''.join([s, repr(d), ')*x^2*y^2;'])
> > ....: magma.eval(s)
> > ....: magma.eval('C:=Curve(P,f);')
> > ....: E = magma('EllipticCurve(C,C![0,1,1])')
> > ....: l = E.aInvariants()
> > ....: EE = EllipticCurve(map(Integer,l))
> > ....: return EE.simon_two_descent()[0]
> > ....:
> > sage: rank(d)
> >
> ---------------------------------------------------------------------------
> > <type 'exceptions.AttributeError'> Traceback (most recent call
> last)
> >
> > /home/zimmerma/<ipython console> in <module>()
> >
> > /home/zimmerma/<ipython console> in rank(d)
> >
> > /usr/local/sage-2.8.12/sage/local/lib/python2.5/site-packages/sage/schemes/elliptic_curves/ell_rational_field.py
> in simon_two_descent(self, verbose, lim1, lim3, limtriv, maxprob,
> limbigprime)
> > 858 (8, 8)
> > 859 """
> > --> 860 if self.torsion_order() % 2 == 0:
> > 861 raise ArithmeticError, "curve must not have rational
> 2-torsion\nThe *only* reason for this is that I haven't finished
> implementing the wrapper\nin this case. It wouldn't be too
> difficult.\nPerhaps you could do it?! Email me ([EMAIL PROTECTED])."
> > 862 F = self.integral_weierstrass_model()
> >
> > /usr/local/sage-2.8.12/sage/local/lib/python2.5/site-packages/sage/schemes/elliptic_curves/ell_rational_field.py
> in torsion_order(self)
> > 1743 return self.__torsion_order
> > 1744 except AttributeError:
> > -> 1745 self.__torsion_order = self.torsion_subgroup
> ().order()
> > 1746 return self.__torsion_order
> > 1747
> >
> > /usr/local/sage-2.8.12/sage/local/lib/python2.5/site-packages/sage/schemes/elliptic_curves/ell_rational_field.py
> in torsion_subgroup(self, flag)
> > 1781 return self.__torsion_subgroup
> > 1782 except AttributeError:
> > -> 1783 self.__torsion_subgroup =
> rational_torsion.EllipticCurveTorsionSubgroup(self, flag)
> > 1784 return self.__torsion_subgroup
> > 1785
> >
> > /usr/local/sage-2.8.12/sage/local/lib/python2.5/site-packages/sage/schemes/elliptic_curves/rational_torsion.py
> in __init__(self, E, flag)
> > 54 G = self.__E.pari_curve().elltors(flag)
> > 55 except RuntimeError:
> > ---> 56 self.__E.__pari_double_prec()
> > 57 if G is None:
> > 58 raise RuntimeError, "Could not compute torsion
> subgroup"
> >
> > <type 'exceptions.AttributeError'>: 'EllipticCurve_rational_field'
> object has no attribute '_EllipticCurveTorsionSubgroup__pari_double_prec'
> >
> > Paul
> >
>
>
>
> --
> William Stein
> Associate Professor of Mathematics
> University of Washington
> http://wstein.org
>
> >
>
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