#11900: Serious regression caused by #9138
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Reporter: SimonKing |
Owner: tbd
Type: defect |
Status: needs_work
Priority: critical |
Milestone: sage-4.8
Component: performance |
Keywords: categories regression
Work_issues: Laurent series rings are fields. CFF is a field. |
Upstream: N/A
Reviewer: Jeroen Demeyer, Nicolas M. Thiéry |
Author: Simon King
Merged: |
Dependencies: #9138 #11911
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Comment(by SimonKing):
Replying to [comment:148 nthiery]:
> Indeed; sorry, I should have posted the patch here since we did not get
to work with the Sage-Combinat queue. Please merge it in your patch as you
feel appropriate.
Meanwhile I wonder whether that change shouldn't better be put on a
different ticket. Namely, using the meet instead of the current algorithm
(recall: The algorithm used in _category_for_hom was used before, I merely
factored it out) actually would change things.
Namely, the meet may return a join category. But the current algorithm for
determining the category for a homset will not return a join category,
unless the categories of both parents coincide.
Example:
{{{
sage: Algebras(QQ)._meet_(Category.join([Fields(), ModulesWithBasis(QQ)]))
Join of Category of rings and Category of vector spaces over Rational
Field
sage: PA = Parent(category=Algebras(QQ))
sage: PJ = Parent(category=Category.join([Fields(),
ModulesWithBasis(QQ)]))
sage: H = Hom(PA,PJ); H
Set of Homomorphisms from <type 'sage.structure.parent.Parent'> to <type
'sage.structure.parent.Parent'>
sage: H.category()
Category of hom sets in Category of rings
sage: H.category().base_category
Category of rings
}}}
Using the meet would be a non-trivial change that probably has little to
do with a speedup. So, better move it to another ticket, isn't it?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11900#comment:149>
Sage <http://www.sagemath.org>
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