#19737: SetPartition.to_permutation().cycle_tuples() is not the identity
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Reporter: mantepse | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-7.0
Component: combinatorics | Resolution:
Keywords: set partitions, | Merged in:
permutations | Reviewers:
Authors: Martin Rubey | Work issues:
Report Upstream: N/A | Commit:
Branch: | c6a3939d2e18efe3906e1f959dc5c019c921a944
u/mantepse/setpartition_to_permutation___cycle_tuples___is_not_the_identity|
Stopgaps:
Dependencies: |
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Comment (by ncohen):
Hello,
> I am not quite convinced that this is true. But if you are convinced,
is there an easy way to do it? Can I simply do
> {{{
> class IntegerSetPartition(SetPartition):
>
> def to_permutation(self):
> ....
>
> }}}
To me such a design would work nicely. And the check that is needed by all
those functions can be performed there:
{{{
class IntegerSetPartition(SetPartition):
def __init__(self, **kwargs):
SetPartition.__init__(self,**kwargs)
assert set(self.base_set()) ==
set(range(self.base_set_cardinality()))
}}}
Or something nicer, which would yield a clearer error message when the
input is wrong.
I believe that this is the way to go. Really, look at the functions of
`SetPartition`: how many are defined for integer partitions *only*? I
don't know much about this kind of combinatorics, but `is_noncrossing`
seems to be of that kind. Hell, I'd even be surprised if less than half of
the methods of `SetPartition` should not be there, or is plain broken
(.N(), .base_extend(), .base_ring(), .count(), db(), .n(),
.numerical_approx(), .rename(), .reset_name(), .subs(), .substitute(),
.version()).
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/19737#comment:19>
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