A Family of Partial Cubes with Minimal Fibonacci Dimension

Abstract

A partial cube G is a graph that admits an isometric embedding into some hypercube Q_k. This implies that vertices of G can be labeled with binary words of length k in a way that the distance between two vertices in the graph corresponds to the Hamming distance between their labels. The minimum k for which this embedding is possible is called the isometric dimension of G, denoted idim(G). A Fibonacci cube Γ_k is the partial cube obtained by deleting all the vertices in Q_k whose labels contain word 11 as factor. It turns out that any partial cube can be always isometrically embedded also in a Fibonacci cube Γ_d. The minimum d is called the Fibonacci dimension of G, denoted fdim(G). In general, idim(G) ≤ fdim(G) ≤ 2 ⋅ idim(G) -1. Despite there is a quadratic algorithm to compute the isometric dimension of a graph, the problem of checking, for a given G, whether idim(G) = fdim(G) is in general NP-complete. An important family of graphs for which this happens are the trees. We consider a kind of generalized Fibonacci cubes that were recently defined. They are the subgraphs of the hypercube Q_k that include only vertices that avoid words in a given set S and are referred to as Q_k(S). We prove some conditions on the words in S to obtain a family of partial cubes with minimal Fibonacci dimension equal to the isometric dimension.