Discussiones Mathematicae Graph Theory 31(3) (2011)
Lehrstuhl II für Mathematik
52056 Aachen, Germany
In this work we show that 4−n ≤ γS(D) ≤ n for each digraph D of order n ≥ 2, and we characterize the digraphs attending the lower bound as well as the upper bound. Furthermore, we prove that γS(D)+dS(D) ≤ n+1 for any digraph D of order n, and we characterize the digraphs D with γS(D)+dS(D) = n+1. Some of our theorems imply well-known results on the signed domination number of graphs.
Keywords: digraph, oriented graph, signed dominating function, signed domination number, signed domatic number.
2010 Mathematics Subject Classification: 05C69.
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Received 29 January 2010
Revised 26 April 2010
Accepted 27 April 2010