On almost invariant subspaces of structural systems and decentralized control

Graph-theoretic conditions are obtained for a structured system to have the property that the supremal L/sub /p-almost invariant (controllability) subspace is generically the entire state space and that the infimal /sup L//sub /p-almost conditional invariant (complementary observability) subspace is generically the zero subspace. The conditions are used to determine stabilizability of structured interconnected systems by means of decentralized feedback control. Although the obtained graph-theoretic conditions are conservative, they are considered satisfactory to the extent that the benefits of easy testability involving only binary calculations outweigh the conservativeness in the results.