Connectivity and Other Invariants of Generalized Products of Graphs

Figueroa-Centeno et al. introduced the following product of digraphs: let D be a digraph and let Γ be a family of digraphs such that V (F ) = V for every F ∈ Γ. Consider any function h : E(D) −→ Γ. Then the product D ⊗h Γ is the digraph with vertex set V (D) × V and ((a, x), (b, y)) ∈ E(D ⊗h Γ) if and only if (a, b) ∈ E(D) and (x, y) ∈ E(h(a, b)). In this paper, we deal with the undirected version of the ⊗h-product, which is a generalization of the classical direct product of graphs and, motivated by the ⊗h-product, we also recover a generalization of the classical lexicographic product of graphs, namely the ◦h-product, that was introduced by Sabidussi en 1961. We provide two characterizations for the connectivity of G ⊗h Γ that generalize the existing one for the direct product. For G ◦h Γ, we provide exact formulas for the connectivity and the edge-connectivity, under the assumption that V (F ) = V , for all F ∈ Γ. We also introduce some miscellaneous results about other invariants in terms of the factors of both, the ⊗h-product and the ◦h-product. Some of them are easily obtained from the corresponding product of two graphs, but many others generalize the existing ones for the direct and the lexicographic product, respectively. We end up the paper by presenting some structural properties. An interesting result is this direction is a characterization for the existence of a nontrivial decomposition of a given graph G in terms of ⊗h-product.