  Synchronization is studied in an array of identical linear oscillators of
arbitrary order, coupled through a dynamic network comprising dissipative
connectors (e.g., dampers) and restorative connectors (e.g., springs). The
coupling network is allowed to contain interior nodes, i.e., those that are not
directly connected to an oscillator. It is shown that the oscillators
asymptotically synchronize if and only if the Schur complement (with respect to
the boundary nodes) of the complex-valued Laplacian matrix representing the
coupling has a single eigenvalue on the imaginary axis.
