Disturbance decoupling and invariant subspaces for delay systems

In this paper we consider the disturbance decoupling problem for distributed parameter systems, with special attention to the case of delay systems. We present several examples which illustrate the difficulties of the infinite dimensional theory for the case of general distributed parameter systems and for the case of delay systems. In this last case we single out a class of subspaces whose invariant properties are easily characterized and which seems to be interesting from the point of view of the applications.This paper has been written according with the research programs of the GNAFA-CNR, with financial support from the Ministero della Pubblica Istruzione.