๐ค AI Summary
This paper introduces the novel concept of a *monitoring arc-geodetic set*โa minimum vertex subset in a directed graph that uniquely identifies every arc via its geodesic paths. Methodologically, it integrates combinatorial graph theory with directed geodesy to derive exact monitoring numbers for several graph classes, including tournaments, DAGs, trees, and bipartite graphs. It establishes NP-completeness for deciding the existence of an arc-geodetic monitoring set of size at most $k$ in directed graphs with maximum degree at most 4, and proves APX-hardness of the general optimization problem. Additionally, it devises an $O(log n)$-approximation algorithm. The work provides a tight combinatorial characterization linking directed graph structure to monitoring coverage, thereby establishing a foundational framework and algorithmic toolkit for extending edge-monitoring theory to the directed setting.