#17096: Implement categories for filtered algebras
-------------------------------------+-------------------------------------
       Reporter:  tscrim             |        Owner:  tscrim
           Type:  enhancement        |       Status:  needs_review
       Priority:  major              |    Milestone:  sage-6.4
      Component:  categories         |   Resolution:
       Keywords:  filtered algebras  |    Merged in:
        Authors:  Travis Scrimshaw   |    Reviewers:
Report Upstream:  N/A                |  Work issues:
         Branch:                     |       Commit:
  public/categories/filtered_algebras-17096|  
8a747c073e706950d1b14e77458539e126ff0550
   Dependencies:                     |     Stopgaps:
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Comment (by darij):

 @nbruin: Thanks for the explanations. So it is what I feared. Someone
 please remove the @cached_methods; it appears there is no easy way to get
 rid of the performance issues.

 Caching these maps relating A to gr(A) on gr(A) was my first idea (and I
 think Travis wanted to implement them as conversions), but it conflicts
 with Travis's design decision (which is a good one!) to allow overriding
 `graded_algebra` with simpler stuff than the default `AssociatedGraded`
 construction. Many different complicated algebras A will end up having the
 same simple gr(A) (for example, for every universal enveloping algebra A =
 U(g) of a Lie algebra g over a field, we have gr(A) \cong S(g)), and gr(A)
 is not supposed to "know" anything about A. Overriding
 `_element_constructor` of gr(A) would be messy and unscalable.

--
Ticket URL: <http://trac.sagemath.org/ticket/17096#comment:66>
Sage <http://www.sagemath.org>
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