# Complexity and approximation ratio of semitotal domination in graphs

Document Type : Original paper

Authors

Guangzhou University

Abstract

A set $S \subseteq V(G)$ is a semitotal dominating set of a graph $G$ if it is a dominating set of $G$ and every vertex in $S$ is within distance 2 of another vertex of $S$. The semitotal domination number $\gamma_{t2}(G)$ is the minimum cardinality of a semitotal dominating set of $G$. We show that the semitotal domination problem is APX-complete for bounded-degree graphs, and the semitotal domination problem in any graph of maximum degree $\Delta$ can be approximated with an approximation ratio of $2+\ln(\Delta-1)$.

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