  For arrays of identical linear systems coupled through relative actuation
four problems are studied: controllability, positive controllability, pairwise
controllability, and positive pairwise controllability. To this end, related to
the eigenvalues of the system matrix, certain graphs with possibly
vector-valued edge weights are constructed. It is shown that array
controllability and graph connectivity are equivalent. Similar equivalences are
established also between positive controllability and strong connectivity,
pairwise controllability and pairwise connectivity, and positive pairwise
controllability and strong pairwise connectivity.
