#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-5.13
Component: elliptic curves | Resolution:
Keywords: simon_two_descent | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
-------------------------------------+-------------------------
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.
New 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which may be caused by the fact that Sage currently uses an outdated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.
--
Comment (by pbruin):
Replying to [comment:1 cremona]:
> There are many similar bug reports with separate trac tickets. I have
no idea if this is a new bug or not. Anyway, the version Sage has of DS's
scripts are not the most recent one so there is no point in reporting this
back to him unless you check that it happens with the scripts on his web
page and you email him without mentioning Sage, otherwise he will just
assume that the problem lies with Sage (which is possible).
I searched for other tickets related to Simon's code and did not find
reports of this particular problem. We should first upgrade to the latest
version of his script and then see which of the various problems listed at
#11041 persist. I added this ticket to that list for easier reference.
--
Ticket URL: <http://trac.sagemath.org/ticket/15483#comment:2>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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