#11474: Elliptic curves should be unique parent structures
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Reporter: SimonKing | Owner: cremona
Type: defect | Status: new
Priority: major | Milestone: sage-4.7.1
Component: elliptic curves | Keywords: unique parent
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by SimonKing):
My approach is:
A) Let `EllipticCurve_generic` inherit from `UniqueRepresentation`. If I
am not mistaken, every other elliptic curve inherits from that, so, that
should be fine.
B) The `__init__` methods should be uniform: ''All'' `__init__` methods
should accept precisely one argument, namely an immutable sequence "ainvs"
(in particular, the underlying field can be obtained from ainvs).
C) By `__classcall__` methods, make sure that the existing ways of
constructing an elliptic curve will still work. In particular, it will
create the immutable sequence "ainv".
One detail to consider: Sometimes an elliptic curve is taken from the
Cremona database (see `sage.schemes.elliptic_curves.ell_rational_field`).
The database provides certain attributes. It is possible that an elliptic
curve ''with the same a-invariant'' is already in the cache, ignorant of
the additional attributes.
But the classcall method could very well assign those additional
attributes to an elliptic curve found in the cache before returning it.
So, it should still work.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11474#comment:1>
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