A 1-planar graph is a graph that can be embedded in the plane with at most one crossing per edge. A 1-planar graph on n vertices can have at most 4n− 8 edges. It is known that testing 1-planarity of a graph is NP-complete. A 1-planar embedding of a graph G is maximal, if no edge can be added without violating the 1-planarity of G. In this paper, we study combinatorial properties of maximal 1-pl...

Let G be a simple connected graph on n vertices and λ1, λ2, . . . , λn be the eigenvalues of the adjacency matrix of G. The Estrada index of G is defined as EE(G) = n i=1 e λi . LetTn be the class of tricyclic graphs G on n vertices. In this paper, the graphs inTn with themaximal Estrada index is characterized. © 2013 Elsevier B.V. All rights reserved.

We present a new energy-minimization framework for the graph isomorphism problem that is based on an equivalent maximum clique formulation. The approach is centered around a fundamental result proved by Motzkin and Straus in the mid-1960s, and recently expanded in various ways, which allows us to formulate the maximum clique problem in terms of a standard quadratic program. The attractive featu...

Abstract Let R be a commutative ring with identity. Let G be a graph with vertices as elements of R, where two distinct vertices a and b are adjacent if and only if there is a maximal ideal of R containing both. In this paper we show that a ring R is finite if and only if clique number of the graph G (associated with R as above) is finite. We also have shown that for a semilocal ring R, the chr...