Aspects of feedback and a local approach for linear systems

The effect of the implementation of constant output feedback on a general rational transfer function matrix has long been of interest. More recently, interest has been shown in the properness of closed-loop systems when such constant output feedback is applied to a general open-loop G(s) which is given either in terms of a state space realisation or as a matrix fraction description. In the first part of this work the effect of constant output feedback on a general composite system is considered and a simple sufficient condition for properness of such a system is derived. [Continues.]