On the first Zagreb index and multiplicative Zagreb coindices of graphs

For a (molecular) graph G with vertex set V (G) and edge set E(G), the first Zagreb index of G is defined as M-1(G) = Sigma v(i is an element of V(G))d(C)(v(i))(2), where d(G) (v(i)) is the degree of vertex v(i), in G. Recently Xu et al. introduced two graphical invariants (Pi) over bar (1) (G) = Pi v(i)v(j is an element of E(G)) (dG (v(i))+dG (v(j))) and (Pi) over bar (2)(G) = Pi(vivj is an element of E(G)) (dG (v(i))+dG (v(j))) named as first multiplicative Zagreb coindex and second multiplicative Zagreb coindex, respectively. The Narumi-Katayama index of a graph G, denoted by NK(G), is equal to the product of the degrees of the vertices of G, that is, NK(G) = Pi(n)(i=1) d(G) (v(i)). The irregularity index t(G) of G is defined as the num=1 ber of distinct terms in the degree sequence of G. In this paper, we give some lower and upper bounds on the first Zagreb index M-1(G) of graphs and trees in terms of number of vertices, irregularity index, maximum degree, and characterize the extremal graphs. Moreover, we obtain some lower and upper bounds on the (first and second) multiplicative Zagreb coindices of graphs and characterize the extremal graphs. Finally, we present some relations between first Zagreb index and NarumiKatayama index, and (first and second) multiplicative Zagreb index and coindices of graphs.Korean Government - 2013R1A1A2009341Necmettin Erbakan ÜniversitesiSelçuk Üniversites

Some properties on the lexicographic product of graphs obtained by monogenic semigroups

In (Das et al. in J. Inequal. Appl. 2013:44, 2013), a new graph Gamma (S-M) on monogenic semigroups S-M (with zero) having elements {0, x, x(2), x(3),..., x(n)} was recently defined. The vertices are the non-zero elements x, x(2), x(3),..., x(n) and, for 1 <= i, j <= n, any two distinct vertices x(i) and x(j) are adjacent if x(i)x(j) = 0 in S-M. As a continuing study, in an unpublished work, some well-known indices (first Zagreb index, second Zagreb index, Randic index, geometric-arithmetic index, atom-bond connectivity index, Wiener index, Harary index, first and second Zagreb eccentricity indices, eccentric connectivity index, the degree distance) over Gamma (S-M) were investigated by the same authors of this paper. In the light of the above references, our main aim in this paper is to extend these studies to the lexicographic product over Gamma (S-M). In detail, we investigate the diameter, radius, girth, maximum and minimum degree, chromatic number, clique number and domination number for the lexicographic product of any two (not necessarily different) graphs Gamma (S-M(1)) and Gamma (S-M(2)).Selçuk ÜniversitesiSungkyunkwan University (BK21

Monojenik yarıgrup graflarının güçlü çarpımlarının bazı graf parametreleri

In Das et al. (2013), it has been defined a new algebraic graph on monogenic semigroups. Our main scope in this study, is to extend this study over the special algebraic graphs to the strong product. In detail, we will determinate some important graph parameters (diameter, girth, radius, maximum degree, minimum degree, chromatic number, clique number and domination number) for the strong product of any two monogenic semigroup graphs.Das ve diğ. (2013) çalışmasında monojenik yarıgruplar üzerinde yeni bir cebirsel graf tanımlanmıştır. Bu çalışmada ana odaklanma noktamız, bu çalışmayı verilen özel cebirsel grafların güçlü çarpımına genişletmektir. Detaylandıracak olursak, herhangi iki monojenik yarıgrup graflarının güçlü çarpımları için bazı önemli graf parametrelerini (çap, çevrim, yarıçap, maksimum derece, minimum derece, renklendirme sayısı, klik sayısı ve baskınlık sayısı) hesaplayacağız

Some graph parameters of power set graphs

In this study, we examine some graph parameters such as the edge number, chromatic number, girth, domination number and clique number of power set graphs