The edge wiener index of suspensions, bottlenecks, and thorny graphs

Let G be a simple connected graph. The distance between the edges g and f E(G) is defined as the distance between the corresponding vertices g and f in the line graph of G. The edge-Wiener index of G is defined as the sum of such distances between all pairs of edges of the graph. Let G1+G2 and G1ο G2 be the join and the corona of graphs G1 and G2, respectively. In this paper, we present explicit formulas for the edge-Wiener index for these graphs. Then we apply our results to compute the edge-Wiener index of suspensions, bottlenecks, and thorny graphs

L(2,1)-labelings of Cartesian products of two cycles

AbstractAn L(2,1)-labeling of a graph is an assignment of nonnegative integers to its vertices so that adjacent vertices get labels at least two apart and vertices at distance two get distinct labels. The λ-number of a graph G, denoted by λ(G), is the minimum range of labels taken over all of its L(2,1)-labelings. We show that the λ-number of the Cartesian product of any two cycles is 6, 7 or 8. In addition, we provide complete characterizations for the products of two cycles with λ-number exactly equal to each one of these values