The configuration space of a robotic arm over a graph

In this paper, we investigate the configuration space S-G,S-b,S-l associated with the movement of a robotic arm of length l on a grid over an underlying graph G, anchored at a vertex b is an element of G. We study an associated poset with inconsistent pairs (PIP) IPG,b,l consisting of indexed paths on G. This PIP acts as a combinatorial model for the robotic arm, and we use IPG,b,l to show that the space S-G,S-b,S-l is a CAT(0) cubical complex, generalizing work of Ardila, Bastidas, Ceballos, and Cuo. This establishes that geodesics exist within the configuration space, and yields explicit algorithms for moving the robotic arm between different configurations in an optimal fashion. We also give a tight bound on the diameter of the robotic arm transition graph - the maximal number of moves necessary to change from one configuration to another - and compute this diameter for a large family of underlying graphs G.