A sharp lower bound for locating-dominating sets in trees

Let LD(G) denote the minimum cardinality of a locating-dominating set for graph G. If T is a tree of order n with l leaf vertices and s support vertices, then a known lower bound of Blidia, Chellali, Maffray, Moncel and Semri [Australas. J. Combin. 39 (2007), 219–232] is LD(T ) ≥ (n+ 1 + l − s)/3 . In this paper, we show that LD(T ) ≥ (n+ 1 + 2(l − s))/3 and these bounds are sharp. We constructively characterize the trees achieving the lower bounds.