Partial detectability and generalized functional observer design for linear descriptor systems

This paper studies linear time-invariant descriptor systems which are not necessarily regular. We introduce the notion of partial detectability and characterize this concept by means of a simple rank criterion involving the system coefficient matrices. Three particular cases of this characterization are discussed in detail. Furthermore, we show that partial detectability is necessary for the existence of a generalized functional observer, but not sufficient. We identify a condition which together with partial detectability gives sufficiency.