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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