Nonobservable and redundant spaces for implicit descriptions

The authors consider continuous linear implicit models, i.e. models which are valid for all time t⩾0. This hypothesis of continuity is needed, for instance, when model reduction is intended. This gives rise to some new interpretations of observability and allows for the introduction of new concepts of redundancy. Geometric characteristics are provided for the nonobservable and the algebraically, differentially, or purely differentially redundant spaces. External minimality is then equivalent to both nonredundancy and observability