Design of state detectors for nonlinear systems using symmetries and semi-invariants

Two techniques are proposed for the design of asymptotic state detectors for nonlinear systems, both in the continuous-time and discrete-time cases. The first technique allows one to design linear state detectors for nonlinear systems belonging to a given class, which is studied and characterized in the paper. The second technique extends the ideas of the first by using semi-invariants to compute invariant sets and study their stability.