  A weak homomorphism from a graph G to a graph H is a mapping f from V(G) to
V(H), where either f(x) = f(y) or {f(x), f(y)} is an element of E(H), and this
holds for all {x, y} in E(G). A rectangular grid graph is formed by taking the
Cartesian product of two paths. In this paper, we present a formula for
calculating the number of weak homomorphisms from paths to rectangular grid
graphs.
