#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 SimonKing):
Replying to [comment:34 pbruin]:
> 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.
... except for the fact that `UniqueFactory` ''alone'' is not enough to
create a unique parent. You need to additionally adapt `__cmp__` etc, and
this is what inheritance from `UniqueRepresentation` does on top of
`__classcall__`.
> 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
This I consider a valid argument for using a factory. But a tad more needs
to be done.
--
Ticket URL: <http://trac.sagemath.org/ticket/11474#comment:35>
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