On a special class of boxicity 2 graphs

TL;DR

This paper introduces 2-stab interval graphs (2SIG), a class with boxicity 2 that extends interval graphs, and demonstrates their chromatic properties, subclasses, and efficient algorithms for clique number computation.

Contribution

It defines 2SIG, explores their properties, bounds their chromatic number relative to clique number, and provides algorithms and characterizations for subclasses.

Findings

Chromatic number of 2SIG is at most twice its clique number.

Efficient algorithms are developed for certain subclasses.

A matrix characterization is provided for a subclass of 2SIG.

Abstract

We define and study a class of graphs, called 2-stab interval graphs (2SIG), with boxicity 2 which properly contains the class of interval graphs. A 2SIG is an axes-parallel rectangle intersection graph where the rectangles have unit height (that is, length of the side parallel to $Y$-axis) and intersects either of the two fixed lines, parallel to the $X$-axis, distance $1+\epsilon$ ($0 < \epsilon < 1$) apart. Intuitively, 2SIG is a graph obtained by putting some edges between two interval graphs in a particular rule. It turns out that for these kind of graphs, the chromatic number of any of its induced subgraphs is bounded by twice of its (induced subgraph) clique number. This shows that the graph, even though not perfect, is not very far from it. Then we prove similar results for some subclasses of 2SIG and provide efficient algorithm for finding their clique number. We provide a matrix characterization for a subclass of 2SIG graph.