#17096: Implement categories for filtered algebras
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       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|  
bb234ec71d1276c6cc14320074b3de6fdc606192
   Dependencies:                     |     Stopgaps:
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Comment (by darij):

 1) What does the `_element_constructor_` in `associated_graded.py` do? I
 understand that it constructs an element of gr A from an element a of A,
 but the way it does this I do not think is correct.

 The "right" thing to do is this: For a given pair `(a, n)` where `n` is a
 nonnegative integer and `a` is an element of the `n`-th filtered part of
 `A`, the residue class of `a` modulo the `(n-1)`-th filtered part of `A`
 is an element of the `n`-th graded component of `\gr A`. The `n` is part
 of the input; you can try to reconstruct it as the smallest `i` such that
 `a` lies in the `i`-th filtered part of `A`, but such a definition will be
 ill-behaved.

 2) I think you need some requirements on the basis of a
 FilteredModulesWithBasis for your code to work. I would guess you want the
 basis to be a sequence `(B_0, B_1, B_2, ...)` of sets such that for every
 `n`, the union `B_0 \cup B_1 \cup ...\cup B_n` is a basis of the `n`-th
 filtered component. Is it what you want?

--
Ticket URL: <http://trac.sagemath.org/ticket/17096#comment:4>
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