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Extremal Combinatorics in Geometry and Graph Theory

Authors: Beagley, Jonathan Edward;

Extremal Combinatorics in Geometry and Graph Theory

Abstract

We study a problem in extremal geometry posed by Paul Erdos and George Szekeres in 1935. This problem is to find the smallest positive integer N(n) such that every point set in general position (no three on a line) of N(n) points contains the vertex set of a convex n-gon. Erdos and Szekeres showed that N(n) exists and conjectured that N(n) = 2n-2 + 1. In 2006, Walter Morris introduced a graph on the copoints of a planar point set in general position, where cliques in the graph correspond to subsets of points in convex position, and showed that the chromatic number of the copoint graph was n if the point set contained at least 2n-2 + 1 points. We extend this copoint graph to abstract convex geometries studied by Edelman and Jamison, where the cliques of this graph are convexly independent sets. A major goal of this dissertation is to study the clique and chromatic numbers for the copoint graph of convex geometries. Much of this dissertation would be trivial if every graph were a copoint graph, so we provide a family of graphs that are not copoint graphs for any convex geometries.

Related Organizations
Keywords

copoint graph, Convex geometry, convex geometry, Order dimension, Happy Ending Problem, order dimension, graph coloring, FOS: Mathematics, 511, Erdos-Szekeres Problem, Mathematics, Copoint graph, Graph coloring

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selected citations
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This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
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