The node cop-win reliability of unicyclic and bicyclic graphs

Various models to quantify the reliability of a network have been studied where certain components of the graph may fail at random and the probability that the remaining graph is connected is the proxy for reliability. In this work we introduce a strengthening of one of these models by considering the probability that the remaining graph is not just connected but also cop-win. A graph is cop-win if one cop can guarantee capture of a fleeing robber in the well-studied pursuit-evasion game of Cops and Robber. More precisely, for a graph $G$ with nodes that are operational independently with probability $p$ and edges that are operational if and only if both of their endpoints are operational, the node cop-win reliability of $G$, denoted $\text{NCRel}(G,p)$, is the probability that the operational nodes induce a cop-win subgraph of $G$. It is then of interest to find graphs $G$ with $n$ nodes and $m$ edges such that $\text{NCRel}(G,p)\ge\text{NCRel}(H,p)$ for all $p\in[0,1]$ and all graphs $H$ with $n$ nodes and $m$ edges. Such a graph is called uniformly most reliable. We show that uniformly most reliable graphs exist for unicyclic and bicyclic graphs, respectively. This is in contrast to the fact that there are no known sparse graphs maximizing the corresponding notion of node reliability.