#16913: Error in prev()
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Reporter: ayyer | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: permutations, | Merged in:
prev | Reviewers:
Authors: André Apitzsch | Work issues:
Report Upstream: N/A | Commit:
Branch: | a2406cd669acf5af044738f24c711b1f5526f3a5
u/aapitzsch/ticket/16913 | Stopgaps:
Dependencies: |
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Comment (by tscrim):
Replying to [comment:2 vdelecroix]:
> One line modification!! great!
>
> - What about `range(n-2,-1,-1)` instead of `reversed(range(0,n-1))`?
+1 as when we switch to python3, the former should be faster (it should be
a hair faster right now anyways).
> - I really would like to see random tests that would prevent this kind
of things happening again
> {{{
> sage: for _ in range(20):
> ....: p = Permutations(randint(2,10)).random_element()
> ....: assert p.next().prev() == p, "problem with p={}".format(p)
> ....: assert p.prev().next() == p, "problem with p={}".format(p)
> }}}
I don't like randomized testing, as errors may not be noticed from the
testing. So a feature gets into Sage which then causes (random) doctest
failures on a clean build. I think a more systematic test (especially in
this case for some small values of n) is better. Yet I do think a larger
test is better to have.
--
Ticket URL: <http://trac.sagemath.org/ticket/16913#comment:3>
Sage <http://www.sagemath.org>
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