#19229: Bug in elliptic curve Galois Representation
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Reporter: cremona | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.9
Component: elliptic curves | Resolution:
Keywords: Galois representations | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by cremona):
Tracked down to {{{_semistable_reducible_primes()}} in line 801:
{{{
F = NumberField(y**2 - a, 'a')
}}}
where a is an integer, but then the code base-changes the base field to
this field Q(sqrt(a)), and there is a problem since 'a' is the name of K's
generator. This causes a ValueError which is caught in the wrong place in
lines 292-4:
{{{
try:
bad_primes = _semistable_reducible_primes(E)
except ValueError:
return [0]
}}}
I will fix this by putting in a test for CM much earlier (which did not
exist when this code was written). Also when constructing F we can make
sure that the name of iots generator is not the same as that of K.
--
Ticket URL: <http://trac.sagemath.org/ticket/19229#comment:1>
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