Observability and State Determination
As is known from measurement theory (cf. section 1.2), the measurement of an observable gives a certain result with a probability depending on the state. This suggests that measurements of appropriate observables on several copies of the same system can be used to determine the state of the system with some level of conﬁdence. In systems theory, the study of the observability of a system describes to what extent it is possible to determine the initial state by a combined action of dynamics and output measurement.