Discussiones Mathematicae Graph Theory 29(1) (2009) 71-86
doi: 10.7151/dmgt.1433

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Johannes H. Hattingh1, Ernst J. Joubert2, Marc Loizeaux3, Andrew R. Plummer4  and  Lucas van der Merwe3

1Department of Mathematics and Statistics
Georgia State University
Atlanta, GA 30303-3083, USA

2Department of Mathematics
University of Johannesburg
P.O. Box 524, Auckland Park 2006, South Africa

3Department of Mathematics
University of Tennessee, Chattanooga
615 McCallie Avenue, Chattanooga, TN 37403, USA

4Department of Linguistics
The Ohio State University
222 Oxley Hall, 1712 Neil Avenue, Columbus, OH 43210, USA


Let G = (V,E) be a graph. A set S ⊆ V is a restrained dominating set if every vertex in V−S is adjacent to a vertex in S and to a vertex in V−S. The restrained domination number of G, denoted by γr(G), is the minimum cardinality of a restrained dominating set of G. A unicyclic graph is a connected graph that contains precisely one cycle. We show that if U is a unicyclic graph of order n, then γr(U) ≥ ⎡[n/3]⎤, and provide a characterization of graphs achieving this bound.

Keywords: restrained domination, unicyclic graph.

2000 Mathematics Subject Classification: 05C69.


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Received 8 November 2007
Revised 6 October 2008
Accepted 6 October 2008