Majority out-dominating sets in digraphs

The concept of majority domination in graphs has been defined in at least two different ways: As a function and as a set. In this work we extend the latter concept to digraphs, while the former was extended in another paper. Given a digraph $D=(V,A),$ a set $S\subseteq V$ is a \textit{majority out-dominating set} (MODS) of $D$ if $|N^+[S]|\geq \frac {n}{2}.$ The minimum cardinality of a MODS in $D$ is the {\it set majority out-domination number} $\gamma^+_{m}(D)$ of $D.$ In this work we introduce these concepts and prove some results about them, among which the characterization of minimal MODSs.