#10998: Categories for posets
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Reporter: nthiery
| Owner: sage-combinat
Type: enhancement
| Status: needs_work
Priority: major
| Milestone: sage-4.7.1
Component: combinatorics
| Keywords: days30, sd31
Work_issues:
| Upstream: N/A
Reviewer: Franco Saliola, Christian Stump, Nicolas M. Thiéry, Florent
Hivert | Author: Frédéric Chapoton, Christian Stump, Nicolas M. Thiéry
Merged:
| Dependencies: #11289, #10938, #9065
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Comment(by hivert):
> Why exactly are posets unique? Isn't it expensive to check that two
posets
> are equivalent? I am interested in dealing with face lattices of about
10^5^
> elements, how long would it take to check their equality? Maybe elements
of
> posets should be unique, but not posets themselves?
As far as I understood, there is not check for equivalence, is it ?
Actually,
I'm not sure what you mean by equivalence opposed to equality. However I
see
no reason why two posets with the same element and the same ordering
should be
different object: mathematically they are the same set with the same
ordering...
More pragmatically, I have some code using poset as key for hash tables.
At
first I didn't ensure that posets were unique then the code end-up
spending
all the time comparing poset that is comparing the underlying graph.
In my opinion, if you need to see two equal poset as different, this is
because you have some more information on those poset (eg: some tag saying
where it come from). If it is the case, I have the feeling that you should
inherit a class from poset which adds the tag and use it for comparison
and
creation so that two differently tagged posets will be different for is as
for
==.
My two cents,
Florent
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10998#comment:37>
Sage <http://www.sagemath.org>
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