#19191: LatticePoset: add is_planar()
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Reporter: jmantysalo | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.9
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Jori Mäntysalo | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jmantysalo/latticeposet__add_is_planar__|
c669ecbf2476518175f0719ba25e76cdc05f1521
Dependencies: | Stopgaps:
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Comment (by jmantysalo):
There seems to be same concept in plain graph theory: ''upward planar''
DAG. See https://en.wikipedia.org/wiki/Upward_planar_drawing
The abstract of first paper I mentioned starts with "It is shown that a
finite lattice is planar if and only if the (undirected) graph obtained
from its (Hasse) diagram by adding an edge between its least and greatest
elements is a planar graph." And this makes no sense if planarity of
lattices would equal to planarity of graphs.
The question is about meaning of Hasse diagram. Should we say that it is a
special type of DAG, or that it is a DAG drawn with a limitation? I think
that writers think about latter.
But of course 1) this must be made very clear in the documentation, and 2)
it might have interesting question in it own to look properties of posets
with planar covering relations graph.
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Ticket URL: <http://trac.sagemath.org/ticket/19191#comment:14>
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