#13240: Give posets polynomials (order, characteristic, zeta, etc.)
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Reporter: csar | Owner: sage-combinat
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.11
Component: combinatorics | Resolution:
Keywords: sd40, days45 | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Alex Csar, Kevin Dilks | Merged in:
Dependencies: | Stopgaps:
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Changes (by ncohen):
* status: needs_review => needs_work
Comment:
Hello !
Would it be possible to add definitions of what these polynomials are,
possibly as links toward wikipedia pages ?
I also think that you should cache minimal and maximal elements in the
code of `remove_top_and_bottom`, otherwise you compute the maximal and
minimal elements for each vertex :
{{{
sage: def a():
....: print "Hey"
....: return [1]
....:
sage: [x for x in range(5) if x in a()]
Hey
Hey
Hey
Hey
Hey
[1]
}}}
Hence if you want to write this function, this really should not be
computed so many times.
Besides : you only implement this method for bounded posets, which means
that there is one max and one min elements. Hence this complicated line
only checks that each vertex is different from two given vertices.
I personally do not think that this `remove_top_and_bottom` method is
useful, especially when it build a copy of the whole poset, which can be
very costly. You would probably save yourself a lot of time if you worked
on `self` in each of your methods, and just ignored the top and bottom
elements. No copies of the poset, no call to `remove_to_and_bottom`
either.
Oh, and Florent thinks that it would be nice to add "seealso" sections
toward "is_bounded", or toward polynomials that are related with each
other.
See youuuuuuuuuuuuuuuuUU !!
Nathann
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13240#comment:19>
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