#15456: fix bug in has_right/left_descents in Weyl group code
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Reporter: | Owner:
zabrocki | Status: needs_review
Type: | Milestone: sage-6.2
defect | Resolution:
Priority: major | Merged in:
Component: | Reviewers:
combinatorics | Work issues:
Keywords: | Commit:
Authors: | 549f238c87e446116457d645c2b0171b423c02df
Frédéric Chapoton | Stopgaps:
Report Upstream: N/A |
Branch: |
u/chapoton/15456 |
Dependencies: |
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Comment (by sdenton):
It's also worth noting that sometimes one 'side' or the other is simply
faster for computing descents. This is clearly true for simple
permutations: one can check in constant time if there's a right descent,
but it takes O(n) to check for a left descent. So then it would be bad
news bears to have a default implementation of the right descent that
calls the left decent.
But in other cases, it's maybe the left descent that's faster to compute,
so you wouldn't want the reverse situation, either...
So I think I would advocate against breaking symmetry at the Category
level, and just raise NotImplemented errors for both sides.
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Ticket URL: <http://trac.sagemath.org/ticket/15456#comment:11>
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