Some bounds on the size of Maximum $G$-free sets in graph

Abstract

For given graph $H$, the independence number $\alpha (H)$ of $H$, is the size of the maximum independent set of $V(H)$. Finding the maximum independent set in a graph is a NP-hard problem. Another version of the independence number is defined as the size of the maximum induced forest of $H$, and called the forest number of $H$, and denoted by $f(H)$. Finding $f(H)$ is also a NP-hard problem. Suppose that $H=(V(H),E(H))$ be a graph, and $\G$ be a family of graphs, a graph $H$ has a $\G$-free $k$-coloring if there exists a decomposition of $V(H)$ into sets $V_i$, $i-1,2,\dots ,k$, so that $G⊈H[V_i]$ for each $i$, and $G\in\G$. $S\subseteq V(H)$ is $G$-free, where the subgraph of $H$ induced by $S$, be $G$-free, i.e. it contains no copy of $G$. Finding a maximum subset of $H$, so that $H[S]$ be a $G$-free graph is a very hard problem as well. In this paper, we study the generalized version of the independence number of a graph. Also giving some bounds about the size of the maximum $G$-free subset of graphs is another purpose of this article.