Some classifications of graphs with respect to a set adjacency relation

Abstract

For any finite simple undirected graph [Formula: see text], we consider the binary relation [Formula: see text] on the powerset [Formula: see text] of its vertex set given by [Formula: see text] if [Formula: see text], where [Formula: see text] denotes the neighborhood of a vertex [Formula: see text]. We call the above relation set adiacence dependency (sa)-dependency of [Formula: see text]. With the relation [Formula: see text] we associate an intersection-closed family [Formula: see text] of vertex subsets and the corresponding induced lattice [Formula: see text], which we call sa-lattice of [Formula: see text]. Through the equality of sa-lattices, we introduce an equivalence relation [Formula: see text] between graphs and propose three different classifications of graphs based on such a relation. Furthermore, we determine the sa-lattice for various graph families, such as complete graphs, complete bipartite graphs, cycles and paths and, next, we study such a lattice in relation to the Cartesian and the tensor product of graphs, verifying that in most cases it is a graded lattice. Finally, we provide two algorithms, namely, the T-DI ALGORITHM and the O-F ALGORITHM, in order to provide two different computational ways to construct the sa-lattice of a graph. For the O-F ALGORITHM we also determine its computational complexity.