ON DISTANCE TWO LABELLING OF UNIT INTERVAL GRAPHS

On Distance Two Labelling of Unit Interval Graphs

An L(2, 1)-labelling of a graph G is an assignment of non-negative integers to the vertices of G such that vertices at distance at most two get different numbers and adjacent vertices get numbers which are at least two apart. The L(2, 1)-labelling number of G, denoted by λ(G), is the minimum range of labels over all such labellings. In this paper, we first discuss some necessary and sufficient ...

M1 internship report: problems on interval graphs L(2,1)-labelling Almost-mixed unit interval graphs

On -unit distance graphs

We consider a variation on the problem of determining the chromatic number of the Euclidean plane and define the -unit distance graph to be the graph whose vertices are the points of E, in which two points are adjacent whenever their distance is within of 1. For certain values of we are able to show that the chromatic number is exactly seven. For some smaller values we show the chromatic number...

Two notions of unit distance graphs

A faithful (unit) distance graph in Rd is a graph whose set of vertices is a finite subset of the d-dimensional Euclidean space, where two vertices are adjacent if and only if the Euclidean distance between them is exactly 1. A (unit) distance graph in Rd is any subgraph of such a graph. In the first part of the paper we focus on the differences between these two classes of graphs. In particula...

Unit Mixed Interval Graphs

In this paper we extend the work of Rautenbach and Szwarcfiter [8] by giving a structural characterization of graphs that can be represented by the intersection of unit intervals that may or may not contain their endpoints. A characterization was proved independently by Joos in [6], however our approach provides an algorithm that produces such a representation, as well as a forbidden graph char...