#15483: Simon 2-descent gives RuntimeError for an elliptic curve over a
quadratic
field
-------------------------------------------------+-------------------------
Reporter: pbruin | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.1
Component: elliptic curves | Resolution:
Keywords: simon_two_descent | Merged in:
Authors: | Reviewers:
Report Upstream: Not yet reported upstream; | Work issues:
Will do shortly. | Commit:
Branch: | Stopgaps:
Dependencies: |
-------------------------------------------------+-------------------------
Description changed by cremona:
Old description:
> The following tries to do 2-descent on an elliptic curve over a quadratic
> field:
> {{{
> K.<s>=QuadraticField(229)
> c4=2173-235*(1-s)/2
> c6=-124369+15988*(1-s)/2
> E=EllipticCurve([-c4/48,-c6/864])
> E.simon_two_descent()
> }}}
> It fails with a `RuntimeError`:
> {{{
> Traceback (most recent call last):
> ...
> RuntimeError:
> *** at top-level: ans=bnfellrank(K,[0,0,0,
> *** ^--------------------
> *** in function bnfellrank: ...eqtheta,rnfeq,bbnf];rang=
> *** bnfell2descent_gen(b
> *** ^--------------------
> *** in function bnfell2descent_gen: ...riv,r=nfsqrt(nf,norm(zc))
> *** [1];if(DEBUGLEVEL_el
> *** ^--------------------
> *** array index (1) out of allowed range [none].
> An error occurred while running Simon's 2-descent program
> }}}
> It appears that a certain number field element is expected to be a
> square, but in fact isn't.
>
> The bug is not fixed by first changing to an integral model.
>
> See #11041 for other bug reports related to Denis Simon's script, some of
> which may be caused by the fact that Sage currently uses an outdated
> version.
New description:
[See #15608 for a list of open simon_two_descent tickets]
The following tries to do 2-descent on an elliptic curve over a quadratic
field:
{{{
K.<s>=QuadraticField(229)
c4=2173-235*(1-s)/2
c6=-124369+15988*(1-s)/2
E=EllipticCurve([-c4/48,-c6/864])
E.simon_two_descent()
}}}
It fails with a `RuntimeError`:
{{{
Traceback (most recent call last):
...
RuntimeError:
*** at top-level: ans=bnfellrank(K,[0,0,0,
*** ^--------------------
*** in function bnfellrank: ...eqtheta,rnfeq,bbnf];rang=
*** bnfell2descent_gen(b
*** ^--------------------
*** in function bnfell2descent_gen: ...riv,r=nfsqrt(nf,norm(zc))
*** [1];if(DEBUGLEVEL_el
*** ^--------------------
*** array index (1) out of allowed range [none].
An error occurred while running Simon's 2-descent program
}}}
It appears that a certain number field element is expected to be a square,
but in fact isn't.
The bug is not fixed by first changing to an integral model.
See #11041 for other bug reports related to Denis Simon's script, some of
which may be caused by the fact that Sage currently uses an outdated
version.
--
--
Ticket URL: <http://trac.sagemath.org/ticket/15483#comment:4>
Sage <http://www.sagemath.org>
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