#11474: Elliptic curves should be unique parent structures
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Reporter: SimonKing | Owner: cremona
Type: defect | Status: needs_info
Priority: major | Milestone: sage-6.3
Component: elliptic curves | Resolution:
Keywords: unique parent | Merged in:
Authors: Simon King | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/defeo/ticket/11474 | 8cbb73e266096e02efc917545aab36d067b7e063
Dependencies: | Stopgaps:
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Comment (by pbruin):
Replying to [comment:33 cremona]:
> Thanks. We need to reach a conclusion while there are other "needs
review" tickets claiming to depend on this. I used to know what that
meant, but now... it may or may not mean that the branches asking for
review include the unreviewed commits here. For example #12880.
I think the other tickets depend on this one in the sense that they need
elliptic curves to be unique parents, not in the sense that they already
include commits that belong to this ticket.
In my opinion we should definitely make elliptic curves unique parents.
The question is whether we should use `UniqueRepresentation` or
`UniqueFactory` (or a custom cache, but I don't see why that would be
needed). I would personally prefer a `UniqueFactory`, mostly because I
think it is more natural and uses less black magic than
`UniqueRepresentation` + `__classcall__`, and hence will be easier to
understand/extend for other developers.
The idea is that the `UniqueFactory` is the place where we do all the work
related to converting various input data into the 5-tuple of
''a''-coefficients. There are ''many'' possible input data, for example:
- ''a''-coefficients
- base ring + ''a''-coefficients
- ''c''-coefficients
- Cremona label
- base ring + Cremona label
- ''j''-invariant
The logic of converting any of these input data into ''a''-coefficients is
very similar for the various base rings, so it seems best to do it all in
one place. I imagine that the future `UniqueFactory` would do the work of
the current (user-level) function
`sage.schemes.elliptic_curves.EllipticCurve` plus the handling of Cremona
labels, which is currently duplicated [triplicated?] in
`EllipticCurve_rational_field`, `EllipticCurve_number_field` and
`EllipticCurve_padic_field`.
Of course, whoever implements this in the end has to make the choice how
to do it. Unfortunately I am currently a bit too busy with some research
things and don't have a lot of time for it at the moment.
--
Ticket URL: <http://trac.sagemath.org/ticket/11474#comment:34>
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