Control issues and linear projection constraints on the control and on the controlled trajectory

Abstract

The goal of this article is to discuss controllability properties for an abstract linear system of the form \(y' = A y + B u\) under some additional linear projection constraints on the control \(u\) or / and on the controlled trajectory \(y\). In particular, we discuss the possibility of imposing the linear projections of the control or / and controlled trajectory, in the context of approximate controllability, exact controllability and null-controllability. As it turns out, in all these settings, for being able to impose linear projection constraints on the control or / and the controlled trajectory, we will strongly rely on a unique continuation property for the adjoint system which, to our knowledge, has not been identified so far, and which does not seem classical. We shall therefore provide several instances in which this unique continuation property can be checked.