Strong geodetic problem on Cartesian products of graphs

The strong geodetic problem is a recent variation of the geodetic problem. For a graph $G$, its strong geodetic number ${\rm sg}(G)$ is the cardinality of a smallest vertex subset $S$, such that each vertex of $G$ lies on a fixed shortest path between a pair of vertices from $S$. In this paper, the strong geodetic problem is studied on the Cartesian product of graphs. A general upper bound for ${\rm sg}(G \,\square\, H)$ is determined, as well as exact values for $K_m \,\square\, K_n$, $K_{1, k} \,\square\, P_l$, and certain prisms. Connections between the strong geodetic number of a graph and its subgraphs are also discussed.Comment: 18 pages, 9 figure

Products of Geodesic Graphs and the Geodetic Number of Products

Given a connected graph and a vertex $x ∈ V (G)$, the geodesic graph $P_x(G)$ has the same vertex set as $G$ with edges $uv$ iff either $v$ is on an $x − u$ geodesic path or $u$ is on an $x − v$ geodesic path. A characterization is given of those graphs all of whose geodesic graphs are complete bipartite. It is also shown that the geodetic number of the Cartesian product of $K_{m,n}$ with itself, where $m, n ≥ 4$, is equal to the minimum of $m, n$ and eight