Bounds relating the weakly connected domination number to the total domination number and the matching number

  • Authors:
  • Johannes H. Hattingh;Michael A. Henning

  • Affiliations:
  • Department of Mathematics and Statistics, Georgia State University, Atlanta, GA 30303-3083, USA;School of Mathematical Sciences, University of KwaZulu-Natal, Pietermaritzburg, 3209, South Africa

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2009

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Abstract

Let G=(V,E) be a connected graph. A dominating set S of G is a weakly connected dominating set of G if the subgraph (V,E@?(SxV)) of G with vertex set V that consists of all edges of G incident with at least one vertex of S is connected. The minimum cardinality of a weakly connected dominating set of G is the weakly connected domination number, denoted @c"w"c(G). A set S of vertices in G is a total dominating set of G if every vertex of G is adjacent to some vertex in S. The minimum cardinality of a total dominating set of G is the total domination number @c"t(G) of G. In this paper, we show that 12(@c"t(G)+1)@?@c"w"c(G)@?32@c"t(G)-1. Properties of connected graphs that achieve equality in these bounds are presented. We characterize bipartite graphs as well as the family of graphs of large girth that achieve equality in the lower bound, and we characterize the trees achieving equality in the upper bound. The number of edges in a maximum matching of G is called the matching number of G, denoted @a^'(G). We also establish that @c"w"c(G)@?@a^'(G), and show that @c"w"c(T)=@a^'(T) for every tree T.