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The paired-domination and the upper paired-domination numbers of graphs

Ulatowski W.

Opuscula Mathematica

2015

Vol. 35, no. 1

127--135

In this paper we continue the study of paired-domination in graphs. A paired-dominating set, abbreviated PDS, of a graph G with no isolated vertex is a dominating set of vertices whose induced subgraph has a perfect matching. The paired-domination number of G, denoted by γP(G), is the minimum cardinality of a PDS of G. The upper paired-domination number of G, denoted by ΓP(G), is the maximum cardinality of a minimal PDS of G. Let G be a connected graph of order n ≥ 3. Haynes and Slater in [Paired-domination in graphs, Networks 32 (1998), 199-206], showed that γ P(G) ≤ n— 1 and they determine the extremal graphs G achieving this bound. In this paper we obtain analogous results for ΓP(G). Dorbec, Henning and McCoy in [Upper total domination versus upper paired-domination, Questiones Mathematicae 30 (2007), 1-12] determine Γp(Pn), instead in this paper we determine Γp(Cn). Moreover, we describe some families of graphs G for which the equality γP(G) = ΓP(G) holds.

All graphs with paired-domination number two less than their order

Ulatowski W.

Opuscula Mathematica

2013

Vol. 33, no. 4

763--783

Let G = (V,E) be a graph with no isolated vertices. A set S ⊆ V is a paired-dominating set of G if every vertex not in S is adjacent with some vertex in S and the subgraph induced by S contains a perfect matching. The paired-domination number Υρ (G) of G is defined to be the minimum cardinality of a paired-dominating set of G. Let G be a graph of order n. In [Paired-domination in graphs, Networks 32 (1998), 199–206] Haynes and Slater described graphs G with Υρ (G) = n and also graphs with Υρ (G) = n − 1. In this paper we show all graphs for which Υρ (G) = n − 2.