Bases in sets and groups and their extremal problems have been studied in additive number theory such as the postage stamp problem. On the other hand, Cayley graphs based on specific finite groups have been studied in algebraic graph theory and applied to construct efficient communication networks such as circulant networks with minimum diameter (or transmission delay). In this paper we establi...

By d(v|G) and d_2(v|G) are denoted the number of first and second neighborsof the vertex v of the graph G. The first, second, and third leap Zagreb indicesof G are defined asLM_1(G) = sum_{v in V(G)} d_2(v|G)^2, LM_2(G) = sum_{uv in E(G)} d_2(u|G) d_2(v|G),and LM_3(G) = sum_{v in V(G)} d(v|G) d_2(v|G), respectively. In this paper, we generalizethe results of Naji et al. [Commun. Combin. Optim. ...

We study extremal questions on induced matchings in certain natural graph classes. We argue that these questions should be asked for twinless graphs, that is graphs not containing two vertices with the same neighborhood. We show that planar twinless graphs always contain an induced matching of size at least n/40 while there are planar twinless graphs that do not contain an induced matching of s...

We consider an extremal problem motivated by a paper of Balogh [J. Balogh, A remark on the number of edge colorings of graphs, European Journal of Combinatorics 27, 2006, 565–573], who considered edge-colorings of graphs avoiding fixed subgraphs with a prescribed coloring. More precisely, given r ≥ t ≥ 2, we look for n-vertex graphs that admit the maximum number of r-edge-colorings such that at...

For a (finite or infinite) family L of oriented graphs, a new parameter called the compressibility number of L and denoted by z(L) is defined. The main motivation is the application of this parameter in a special case of Turán-type extremal problems for digraphs, in which it plays the role of chromatic number in the classic extremal problems. We estimate this parameter for some special group of...

Using a heuristic optimization module based upon Variable Neighborhood Search (VNS), the system AutoGraphiX’s main feature is to find extremal or near extremal graphs, i.e., graphs that minimize or maximize an invariant. From the so obtained graphs, conjectures are found either automatically or interactively. Most of the features of the system relies on the optimization that must be efficient b...

All graphs in this paper are understood to be finite, undirected, without loops or multiple edges. The graph G' = (V', E') is called an induced subgraph of G = (V, E) if V' ~ V and uv E E' if and only if {u, v} ~ V', uv E E. The following two problems about induced matchings have been formulated by Erdos and Nesetril at a seminar in Prague at the end of 1985: 1. Determine f(k, d), the maximum n...