EXACT CONTROLLABILITY, STABILIZATION AND PERTURBATIONS FOR DISTRIBUTED SYSTEMS

Exact controllability is studied for distributed systems, of hyperbolic type or for Petrowsky systems (like plate equations). The control is a boundary control or a local distributed control. Exact controllability consists in trying to drive the system to rest in a given finite time. The solution of the problems depends on the function spaces where the initial data are taken, and also depends on the function space where the control can be chosen. A systematic method (named HUM, for Hilbert Uniqueness Method) is introduced. It is based on uniqueness results (classical or new) and on Hilbert spaces constructed (in infinitely many ways) by using Uniqueness. A number of applications are indicated. Nonlinear Riccati type PDEs are obtained. Finally, we consider how all this behaves for perturbed systems.