The $k$-distance mutual-visibility problem in graphs

TL;DR

This paper introduces the $k$-distance mutual-visibility problem in graphs, extending the classical concept to account for limited visibility range, and explores its computational complexity, properties, bounds, and specific cases.

Contribution

It defines the $k$-distance mutual-visibility number, proves NP-completeness of the decision problem, and provides properties, bounds, and exact values for certain graph classes.

Findings

The decision problem is NP-complete.

Derived tight bounds for the $k$-distance mutual-visibility number.

Exact values computed for specific graph classes.

Abstract

The concept of mutual visibility in graphs, introduced recently, addresses a fundamental problem in Graph Theory concerning the identification of the largest set of vertices in a graph such that any two vertices have a shortest path connecting them, excluding internal vertices of the set. Originally motivated by some challenges in Computer Science related to robot navigation, the problem seeks to ensure unobstructed communication channels between navigating entities. The mutual-visibility problem involves determining a largest mutual-visibility set in a graph. The mutual-visibility number of a graph represents the cardinality of the largest mutual-visibility set. This concept has sparked significant research interest, leading to connections with classical combinatorial problems like the Zarankiewicz problem and Tur\'an-type problems. In this paper, we consider practical limitations in network visibility and our investigation extends the original concept to $k$-distance mutual-visibility. In this case, a pair of vertices is considered $S$-visible if a shortest path of length at most $k$ exists, excluding internal vertices belonging to the set $S$. The $k$-distance mutual-visibility number represents the cardinality of a largest $k$-distance mutual-visibility set. We initiate the study of this new graph parameter. We prove that the associate decision problem belongs to the NP-complete class. We also give some properties and tight bounds, as well as, the exact value of such parameter for some particular non trivial graph classes.