Domination games played on line graphs of complete multipartite graphs

Abstract

The domination game on a graph $G$ (introduced by B. Bre\v{s}ar, S. Klav\v{z}ar, D.F. Rall \cite{BKR2010}) consists of two players, Dominator and Staller, who take turns choosing a vertex from $G$ such that whenever a vertex is chosen by either player, at least one additional vertex is dominated. Dominator wishes to dominate the graph in as few steps as possible, and Staller wishes to delay this process as much as possible. The game domination number $\gamma _{{\small g}}(G)$ is the number of vertices chosen when Dominator starts the game; when Staller starts, it is denoted by $\gamma _{{\small g}}^{\prime }(G).$ In this paper, the domination game on line graph $L\left( K_{\overline{m}}\right) $ of complete multipartite graph $K_{\overline{m}}$ $(\overline{m}\equiv (m_{1},...,m_{n})\in \mathbb{N} ^{n})$ is considered, the exact values for game domination numbers are obtained and optimal strategy for both players is described. Particularly, it is proved that for $m_{1}\leq m_{2}\leq ...\leq m_{n}$ both $\gamma _{{\small g}}\left( L\left( K_{\overline{m}}\right) \right) =\min \left\{ \left\lceil \frac{2}{3}\left\vert V\left( K_{\overline{m}}\right) \right\vert \right\rceil ,\right.$ $\left. 2\max \left\{ \left\lceil \frac{1}{2}\left( m_{1}+...+m_{n-1}\right) \right\rceil ,\text{ }m_{n-1}\right\} \right\} -1$ when $n\geq 2$ and $\gamma _{g}^{\prime }(L\left( K_{\overline{m}}\right) )=\min \left\{ \left\lceil \frac{2}{3}\left( \left\vert V(K_{_{\overline{m}}})\right\vert -2\right) \right\rceil ,\right.$ $\left. 2\max \left\{ \left\lceil \frac{1}{2}\left( m_{1}+...+m_{n-1}-1\right) \right\rceil ,\text{ }m_{n-1}\right\} \right\} $ when $n\geq 4$.