#18031: Bug in saturation for elliptic curves over Q
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Reporter: cremona | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: elliptic curves | Resolution:
Keywords: saturation | Merged in:
Authors: John Cremona | Reviewers:
Report Upstream: Fixed upstream, but not in a | Work issues:
stable release. | Commit:
Branch: | Stopgaps:
Dependencies: |
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Description changed by cremona:
Old description:
> A bug in eclib's saturation function is revealed here:
> {{{
> sage: E = EllipticCurve([0,-1,1,-266,968])
> sage: Q1 = E([-1995,3674,125])
> sage: Q2 = E([157,1950,1])
> sage: E.saturation([Q1,Q2])
> ([(-399/25 : 3674/125 : 1), (157 : 1950 : 1)], 1, 7.21429780216482)
> sage: P1, P2 = E.gens()
> sage: E.regulator()
> 0.801588644684980
> sage: E.regulator_of_points([Q1,Q2])
> 7.21429780216482
> }}}
> The points Q1,Q2 generate a subgroup of index 3 but the computed bound on
> the index is between 2 and 3. This will be fixed upstream.
>
> Note that for this curve E.gens() gives correct generators but
> E.simon_two_descent() gives the above two points.
New description:
A bug in eclib's saturation function is revealed here:
{{{
sage: E = EllipticCurve([0,-1,1,-266,968])
sage: Q1 = E([-1995,3674,125])
sage: Q2 = E([157,1950,1])
sage: E.saturation([Q1,Q2])
([(-399/25 : 3674/125 : 1), (157 : 1950 : 1)], 1, 7.21429780216482)
sage: P1, P2 = E.gens()
sage: E.regulator()
0.801588644684980
sage: E.regulator_of_points([Q1,Q2])
7.21429780216482
}}}
The points Q1,Q2 generate a subgroup of index 3 but the computed bound on
the index is between 2 and 3. This will be fixed upstream.
Note that for this curve E.gens() gives correct generators but
E.simon_two_descent() gives the above two points.
New upstream source at
[http://boxen.math.washington.edu/home/cremona/eclib-20150323.tar.bz2]
--
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Ticket URL: <http://trac.sagemath.org/ticket/18031#comment:2>
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