Abstract. A set of vertices S resolves a connected graph G if every vertex is uniquely determined by its vector of distances to the vertices in S. The metric dimension of G is the minimum cardinality of a resolving set of G. Let G β,D be the set of graphs with metric dimension β and diameter D. It is well-known that the minimum order of a graph in G β,D is exactly β + D. The first contribution of this paper is to characterise the graphs in G β,D with order β + D for all values of β and D. Such a characterisation was previously only known for D ≤ 2 or β ≤ 1. The second contribution is to determine the maximum order of a graph in G β,D for all values of D and β. Only a weak upper bound was previously known.
IntroductionLet G be a connected graph 1 . A vertex x ∈ V (G) resolves 2 a pair of vertices v, w ∈ V (G) if dist(v, x) = dist(w, x). A set of vertices S ⊆ V (G) resolves G, and S is a resolving set of G, if every pair of distinct vertices of G are resolved by some vertex in S. Informally, S resolves G if every vertex of G is uniquely determined by its vector of distances to the 2000 Mathematics Subject Classification. 05C12 (distance in graphs), 05C35 (extremal graph theory). Key words and phrases. graph, distance, resolving set, metric dimension, metric basis, diameter, order. The research of Carmen Hernando, Mercè Mora, Carlos Seara, and David Wood is supported by the projects MEC MTM2006-01267 and DURSI 2005SGR00692. The research of Ignacio Pelayo is supported by the projects MTM2005-08990-C02-01 and SGR2005-00412. The research of David Wood is supported by a Marie Curie Fellowship of the European Community under contract 023865.1 Graphs in this paper are finite, undirected, and simple. The vertex set and edge set of a graph G are denoted by V (G) and, is the length (that is, the number of edges) in a shortest path between v and w in G. The eccentricity of a vertex v in G is eccG(v) := max{distG(v, w) : w ∈ V (G)}. We drop the subscript G from these notations if the graph G is clear from the context. The diameter2 It will be convenient to also use the following definitions for a connected graph G. A vertex x ∈ V (G)resolves a set of vertices T ⊆ V (G) if x resolves every pair of distinct vertices in T . A set of vertices S ⊆ V (G) resolves a set of vertices T ⊆ V (G) if for every pair of distinct vertices v, w ∈ T , there exists a vertex x ∈ S that resolves v, w. [2,3,4,5,6,7,9,17,19,20,21,22,23,24,25,26,27,29,31,32,33], and arise in diverse areas including coin weighing problems [10,14,16,18,30], network discovery and verification [1], robot navigation [17,27], connected joins in graphs [26], the Djoković-Winkler relation [3], and strategies for the Mastermind game [8,11,12,13,16].For positive integers β and D, let G β,D be the class of connected graphs with metric dimension β and diameter D. Consider the following two extremal questions:• What is the minimum order of a graph in G β,D ?• What is the maximum order of a graph in G β,D ?The first question was independently answered by Yushmanov [33], Khuller ...