An Extremal Problem in Distance-\(k\) Domination

Mark S. Anderson1, Robert C. Brigham2, Julie R. Carrington1, Richard P. Vitray1, Donna J. Williams3, Jay Yellen1
1Department of Mathematical Sciences, Rollins College, Winter Park FL 32789
2Department of Mathematics, University of Central Florida, Orlando FL 32816
3Department of Computer Science, Wake Forest University Winston-Salem NC 27109

Abstract

The distance-\( k \) domination number of graph \( G \), \( \gamma_{\leq k}(G) \), is the cardinality of a smallest set of vertices, \( S \), such that every vertex not in \( S \) is no more than distance \( k \) from at least one vertex of \( S \). Carrington, Harary, and Haynes showed \( |V^0| \geq 2|V^+| \) where \( V^0 = \{u \in V: \gamma_{\leq 1}(G-v) = \gamma_{\leq 1}(G)\} \) and \( V^+ = \{v \in V: \gamma_{\leq 1}(G-v) > \gamma_{\leq 1}(G)\} \). This paper extends the result to distance-\( k \) domination, with the obvious change in definition of \( V^0 \) and \( V^+ \), to show \( |V^0| \geq \frac{2}{2k-1}|V^+| \). Extremal graphs are characterized when \( k = 1 \) and some progress is mentioned on the characterization problem when \( k > 1 \).