#10667: Morphisms and Objects of Categories
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Reporter: SimonKing | Owner: nthiery
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.0
Component: categories | Keywords: objects morphisms
containment
Work_issues: Cartesian products | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #9138, #11115, #11780
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Comment(by SimonKing):
Replying to [comment:50 nthiery]:
> Replying to [comment:43 SimonKing]:
> I am not absolutely sure about this: as for parents, it is recommended
> for Homsets to have unique representation, but I am not sure this is
> currently *required* and *enforced*.
First of all, Homsets ''are'' cached. But using unique representation, it
is less easy to break the cache.
And I think that we should use any opportunity to reduce the number of
violations of the unique parent assumption. After all, it is a matter of
efficiency.
> This might be the issue you
> encountered with polynomials.
Actually it was. The problem was that (for the sake of explicit
documentation) some tests create a polynomial ring directly, not using the
`PolynomialRing` constructor. My solution: I introduced a parent method
for rings, that removes the ring from the homset cache, and use it after
any test that creates a non-unique parent. Of course, it is for internal
use only.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10667#comment:51>
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