the second minimum of the irregularity of graphs

3 downloads 118 Views 57KB Size Report
The word graph refers to a finite, undirected graph without loops and multiple edges. For a graph G, Albertson has defined the irregularity of G as irr(G)=. | ( ).
5th Conference on Algebraic Combinatorics and Graph Theory, July 3 4, 2012

THE SECOND MINIMUM OF THE IRREGULARITY OF GRAPHS R. Nasiri-Gharghani1 and G. H. Fath-Tabar2 1

Department of Mathematics, University of Qom, Qom, Islamic Republic of Iran 2 Department of Pure Mathematics, Faculty of Mathematical Sciences, University of Kashan, Kashan 87317-51167, I. R. Iran

Abstract

The word graph refers to a finite, undirected graph without loops and multiple edges. For a graph G, Albertson has defined the irregularity of G as irr(G)=

| ( )

( )| where

d(u) is the degree of vertex u. Recently, this graph invariant gained interest in chemical graph theory. In this work, we present some new result on the second minimum of the irregularity of graphs.

Theorem 1. Let G be a graph then Irr(G) is only even number. Corollary 2. The second minimum of the irregularity of a graph is 2. Theorem 3. There are 25 types of graphs with irregularity of 2.

References 1. M. O. Albertson, The irregularity of a graph, Ars Comb. 46 (1997) 219 225. 2. G. H. Fath Tabar, B. Furtula and I. Gutman, A new geometric-arithmetic index, J. Math. Chem. 47 (2010) 477 486. 3. G. H. Fath Tabar, Old and new Zagreb index, MATCH Commun. Math.Comput. Chem. 65 (2011)79 84.

[32]

Suggest Documents