#12876: Fix element and parent classes of Hom categories to be abstract, and
simplify the Hom logic.
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Reporter: nthiery | Owner: nthiery
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.4
Component: categories | Resolution:
Keywords: categories, Hom | Work issues: add commit message
to one patch
Report Upstream: N/A | Reviewers: Simon King
Authors: Nicolas M. Thiéry | Merged in:
Dependencies: #11521, #12215, #12313 | Stopgaps:
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Comment (by nthiery):
Hi Simon,
Sorry, I am slow answering; I was immersed all afternoon in tracking
down a nasty bug where UniqueRepresentation was violated. It turned
out that the UniqueRepresentation dict had to equal entries in its
keys (gasp), and that was due to a tricky mro order for a non trivial
inheritance involving Category_singleton and FastHash which got the
hash to change over time ... Anyway ...
Replying to [comment:68 SimonKing]:
> {{{
> Diagonal functions can be constructed using the ``diagonal`` option::
>
> sage: X = CombinatorialFreeModule(QQ, [1,2,3,4]); X.rename("X")
> sage: Y = CombinatorialFreeModule(QQ, [1,2,3,4], key="Y");
Y.rename("Y")
> sage: H = Hom(X, Y)
> }}}
> Why are X and Y renamed? There is yet another location where things are
renamed, namely
> Here, I also wonder about the "key" argument.
I do this fairly systematically in the tests in modules_with_basis. It
makes it immediate to check that the domain and codomain are set
properly when looking at the repr of a morphism or homset. They key is
to force the domain and codomain to be distinct (otherwise, and this
happened to me, if the code accidently interchanges the two it will
get unnoticed).
Well, and for good or bad, once you rename a given parent in a
doctest, you have to rename consistently this parent in all other
doctests in the same file. Or to call X.rename() at the end of the
doctest.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12876#comment:74>
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