#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. Add docs. Don't use is_ring and
friends | Upstream: N/A
Reviewer: Jeroen Demeyer, Nicolas M. Thiéry
| Author: Simon King
Merged:
| Dependencies: #9138 #11911
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Comment(by SimonKing):
Hmm. This will be more difficult than I thought: There are lots of
`is_field` methods in Sage. Apparently some of them are not cached. It
would probably not be feasible to have a custom `category()` method in all
cases.
What could one do instead?
I see the following options:
1. We could remove the custom `__contains__` method and restrict
ourselves to fixing the case of `PolynomialQuotientRing` in the way I
indicated. After all, this is the only case of failing doctests.
1. We could remove the custom `__contains__` method and the category
stuff for all parents with an `is_field()` method.
1. We could preserve the custom `__contains__` method of `Fields()`, but
ensure that the potentially time-consuming additional tests are cached.
Instead of caching all `is_field()` methods (there are quite many), I
suggest to use a cache on the function `sage.rings.field.is_Field`.
Namely, this is what is really called in the custom `__contains__` method.
I think the first solution is not really a solution. The second is too
much for this ticket. The third seems fine to me, though. What do you
think?
In more detail: We introduce the `_refine_category()` method to
`CategoryObject`. We impose a cache on `sage.rings.field.is_Field`. In
`sage.rings.field.is_Field`, we use `_refine_category()` on those rings
that were found to be a field.
Since `is_Field` is cached, the `_refine_category()` method will be called
at most once, and `sage.categories.fields.Fields.__contains__` will also
be faster because of the cache.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11900#comment:118>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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