Trees with equal total domination and 2-rainbow domination numbers

Abstract

A 2-rainbow dominating function (2RDF) of a graph G is a function f : V(G) ? P({1,2}) such that for each v ? V(G) with f (v) = ? we have Uu?N(v) f (u) = {1,2}. For a 2RDF f of a graph G, the weight w(f) of f is defined as w(f)=?v?V(G)?f(v)?. The minimum weight over all 2RDFs of G is called the 2-rainbow domination number of G, which is denoted by ?r2(G). A subset S of vertices of a graph G without isolated vertices, is a total dominating set of G if every vertex in V(G) has a neighbor in S. The total domination number ?t(G) is the minimum cardinality of a total dominating set of G. Chellali, Haynes and Hedetniemi conjectured that ?t(G)? ?r2(G) [M. Chellali, T.W. Haynes and S.T. Hedetniemi, Bounds on weak Roman and 2-rainbow domination numbers, Discrete Appl. Math. 178 (2014), 27-32.], and later Furuya confirmed the conjecture [M. Furuya, A note on total domination and 2-rainbow domination in graphs, Discrete Appl. Math. 184 (2015), 229-230.]. In this paper, we provide a constructive characterization of trees T with ?r2(T) = ?t(T).