#15283: Rowmotion and Panyushev orbits: iterators for orbits and better doc
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Reporter: darij | Owner:
Type: enhancement | Status:
Priority: major | positive_review
Component: combinatorics | Milestone: sage-5.13
Keywords: posets, rowmotion, sage- | Resolution:
combinat, panyushev, order-ideals, categories | Merged in:
Authors: Darij Grinberg | Reviewers: Nathann
Report Upstream: N/A | Cohen
Branch: | Work issues:
Dependencies: | Commit:
| Stopgaps:
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Comment (by nbruin):
Replying to [comment:10 darij]:
> I don't think {{{self.lt}}} returns the right format for {{{sorted}}}.
It seems that the {{{cmp}}} keyword of {{{sorted}}} wants a total
-1,0,1-valued function, not a boolean one. See how this prints the same
list twice:
> {{{
> P = Poset({i: divisors(i) for i in divisors(24)})
> print sorted(list(P), cmp=P.lt)
> print sorted(list(P), cmp=P.gt)
> }}}
The recommended way is to use `sorted(...,key=...)` where `key` should map
the sequence elements into a totally ordered set (for instance, the
integers). This provides a concise way of the decorate-sort-undecorate
pattern, or ''Schwartzian transform'', which is generally more efficient
than sorting with a likely expensive custom sort function.
The `cmp` keyword is actually removed in Python 3. See
`functools.cmp_to_key` to convert a legitimate `cmp` function into a value
suitable for `key`.
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Ticket URL: <http://trac.sagemath.org/ticket/15283#comment:16>
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