Complexity and Computation of Connected Zero Forcing

TL;DR

This paper investigates the complexity and structural properties of connected zero forcing sets in graphs, establishing NP-hardness, characterizing specific graph classes, and linking these sets to matroids and greedoids.

Contribution

It proves NP-hardness for connected zero forcing set problems, provides structural characterizations, and identifies graph families where these sets form matroids and greedoids.

Findings

NP-hardness of connected zero forcing set problem

Structural results relating to graph density and induced subgraphs

Connected zero forcing sets form matroids and greedoids in certain graph families

Abstract

Zero forcing is an iterative graph coloring process whereby a colored vertex with a single uncolored neighbor forces that neighbor to be colored. It is NP-hard to find a minimum zero forcing set - a smallest set of initially colored vertices which forces the entire graph to be colored. We show that the problem remains NP-hard when the initially colored set induces a connected subgraph. We also give structural results about the connected zero forcing sets of a graph related to the graph's density, separating sets, and certain induced subgraphs, and we characterize the cardinality of the minimum connected zero forcing sets of unicyclic graphs and variants of cactus and block graphs. Finally, we identify several families of graphs whose connected zero forcing sets define greedoids and matroids.