#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 | Keywords: saturation
curves | Authors: John Cremona
Merged in: | Report Upstream: Reported upstream. Developers
Reviewers: | acknowledge bug.
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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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.
--
Ticket URL: <http://trac.sagemath.org/ticket/18031>
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