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String graphs and incomparability graphs

Published: 17 June 2012 Publication History

Abstract

Given a collection C of curves in the plane, its string graph is defined as the graph with vertex set C, in which two curves in C are adjacent if and only if they intersect. Given a partially ordered set (P,<), its incomparability graph is the graph with vertex set P, in which two elements of P are adjacent if and only if they are incomparable.
It is known that every incomparability graph is a string graph. For "dense" string graphs, we establish a partial converse of this statement. We prove that for every ε>0 there exists δ>0 with the property that if C is a collection of curves whose string graph has at least ε |C|2 edges, then one can select a subcurve γ' of each γ ∈ C such that the string graph of the collection {γ':γ ∈ C} has at least δ |C|2 edges and is an incomparability graph. We also discuss applications of this result to extremal problems for string graphs and edge intersection patterns in topological graphs.

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    cover image ACM Conferences
    SoCG '12: Proceedings of the twenty-eighth annual symposium on Computational geometry
    June 2012
    436 pages
    ISBN:9781450312998
    DOI:10.1145/2261250
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    Published: 17 June 2012

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    1. incomparability graphs
    2. perfect graphs
    3. string graphs

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    SoCG '12
    SoCG '12: Symposium on Computational Geometry 2012
    June 17 - 20, 2012
    North Carolina, Chapel Hill, USA

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