Permutational Powers of a Graph

Abstract

This paper introduces a new graph construction, the permutational power of a graph, whose adjacency matrix is obtained by the composition of a permutation matrix with the adjacency matrix of the graph. It is shown that this construction recovers the classical zig-zag product of graphs when the permutation is an involution, and it is in fact more general. We start by discussing necessary and sufficient conditions on the permutation and on the adjacency matrix of a graph to guarantee their composition to represent an adjacency matrix of a graph, then we focus our attention on the cases in which the permutational power does not reduce to a zig-zag product. We show that the cases of interest are those in which the adjacency matrix is singular. This leads us to frame our problem in the context of equitable partitions, obtained by identifying vertices having the same neighborhood. The families of cyclic and complete bipartite graphs are treated in details. (2010): 05C50, 05C76, 05C78. Mathematics Subject Classification

Enumerating conjugacy classes of graphical groups over finite fields

“…It is natural to consider other graph operations beyond disjoint unions and joins. Preliminary experimental evidence indicates that it might be worthwhile to study the effect of taking permutational powers [4] (including the famous zig-zag products [20] which they generalise) on the polynomials C Γ (X, Y ).…”