#4061: coercion from torsion subgroup of elliptic curve to elliptic curve is
broken
---------------------------+------------------------------------------------
Reporter: was | Owner: was
Type: defect | Status: new
Priority: minor | Milestone: sage-3.2.1
Component: number theory | Resolution:
Keywords: |
---------------------------+------------------------------------------------
Changes (by mabshoff):
* cc: cremona (added)
Comment:
This is still a problem in Sage 3.2.1.alpha2:
{{{
----------------------------------------------------------------------
| Sage Version 3.2.1.alpha2, Release Date: 2008-11-26 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: E = EllipticCurve([0,1,0,72,-368]); E
Elliptic Curve defined by y^2 = x^3 + x^2 + 72*x - 368 over Rational
Field
sage: T = E.torsion_subgroup(); T
Torsion Subgroup isomorphic to Multiplicative Abelian Group isomorphic to
C6 associated to the Elliptic Curve defined by y^2 = x^3 + x^2 + 72*x -
368 over Rational Field
sage: [n*T.0 for n in range(6)]
[(0 : 1 : 0),
(36 : 224 : 1),
(8 : 28 : 1),
(4 : 0 : 1),
(8 : -28 : 1),
(36 : -224 : 1)]
sage: [E(z) for z in T]
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/scratch/mabshoff/release-cycle/sage-3.2.1.alpha3/<ipython console> in
<module>()
/scratch/mabshoff/release-cycle/sage-3.2.1.alpha3/local/lib/python2.5
/site-packages/sage/schemes/elliptic_curves/ell_generic.pyc in
__call__(self, *args, **kwds)
505 ell_point.EllipticCurvePoint)):
506 args = tuple(args[0])
--> 507 return plane_curve.ProjectiveCurve_generic.__call__(self,
*args, **kwds)
508
509 def is_x_coord(self, x):
/scratch/mabshoff/release-cycle/sage-3.2.1.alpha3/local/lib/python2.5
/site-packages/sage/schemes/generic/scheme.pyc in __call__(self, *args)
180 else:
181 return self.point(S)
--> 182 return self.point(args)
183
184 def point_homset(self, S = None):
/scratch/mabshoff/release-cycle/sage-3.2.1.alpha3/local/lib/python2.5
/site-packages/sage/schemes/generic/scheme.pyc in point(self, v, check)
213
214 def point(self, v, check=True):
--> 215 return self._point_class(self, v, check=check)
216
217 def _point_class(self):
/scratch/mabshoff/release-cycle/sage-3.2.1.alpha3/local/lib/python2.5
/site-packages/sage/schemes/elliptic_curves/ell_point.pyc in
__init__(self, curve, v, check)
190 "Argument v (= %s) must be a scheme point,
list, or tuple."%str(v)
191 if len(v) != d and len(v) != d-1:
--> 192 raise TypeError, "v (=%s) must have %s
components"%(v, d)
193 v = Sequence(v, point_homset.value_ring())
194 if len(v) == d-1: # very common special case
TypeError: v (=(1,)) must have 3 components
}}}
I am adding John to the CC field - maybe he has some insight here.
Cheers,
Michael
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4061#comment:1>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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