#16806: Isogeny Bounds for Elliptic Curves over Number Fields
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Reporter: elarson3 | Owner:
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-feature
Component: elliptic curves | Resolution:
Keywords: | Merged in:
Authors: Eric Larson | Reviewers: John Cremona
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/cremona/ticket/16806 | 828ed6fee261a575c27e996d84c11c2bc7dabac0
Dependencies: | Stopgaps:
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Comment (by cremona):
Replying to [comment:14 wuthrich]:
> A few comments:
> * The docstring of the main function reads ""Returns a list of primes
`p` including all primes for which the mod-`p` representation might not be
contained in a Borel."" Isn't it the complement, i.e., all those that "may
be contained in a Borel" ?
>
You are right.
> * I thought "try: ... except {{{ValueError}}}: return [0]" is not
what we should do. If the long and convoluted line in try produces a
{{{ValueError}}}, that could have many reasons, and we should not just
ignore this and send back [0] but pass the error on.
I'm to blame for the long line -- the original version had this split over
many lines. The set we return is the union of (1) primes of additive
reduction (found as factors of gcd(c4,Delta) in effect; (2) primes
ramified in the field; (3) the ones returned by
_semistable_reducible_primes. The latter function uses [0] to denote CM.
So I cannot see what circumstances will lead to a ValueError, and suggest
we can simplify this.
>
> * It is a shame that this function will not be available for curves over
Q. But I guess it should be a separate ticket to merge the two classes
dealing with Galois Reps together at some point.
Agreed. I said so myself somewhere.
I will revise the branch to take into account your first two points...
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Ticket URL: <http://trac.sagemath.org/ticket/16806#comment:15>
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