On maximizing private neighbors in graphs

TL;DR

This paper introduces new graph parameters focused on maximizing private neighbors of various types within vertex sets, generalizing existing concepts like independence and domination.

Contribution

It defines and studies new maximization parameters related to private neighbors, extending classical graph parameters such as independence and domination.

Findings

New parameters generalize known graph invariants.

Characterization of optimal sets for maximizing private neighbors.

Connections established between private neighbor maximization and existing graph parameters.

Abstract

Given a set $U \subset V$ of vertices in a graph $G = (V, E)$, a {\it private neighbor with respect to the set $U$} is any vertex $w \in V$ having precisely one neighbor, say $v$, in $U$. If $w \in V - U$, then $w$ is called an {\it external private neighbor} of $v$ with respect to $U$. If $w \in U$ then $w$ is called an {\it internal private neighbor} of $v$ with respect to $U$. We also add one special case: if $w \in U$ and $N(w) \cap U = \emptyset$, then we say that $w$ is a {\it self private neighbor} with respect to $U$. By definition, a self private neighbor with respect to $U$ is an isolated vertex in the subgraph of $G$ induced by $U$. In this paper we consider the general problems of trying to find sets of vertices which maximize the number of private neighbors of specific types in a graph. In the process of doing this we define several new maximization parameters of graphs which generalize some known and well-studied parameters of graphs relating to vertex and edge independence, domination and irredundance in graphs.