Structural delay-1 input-and-state observability

This paper studies structured discrete-time LTI systems, where the state-space matrices have a fixed zero pattern, and all other entries are free parameters. The goal is to obtain generic results, true for almost all values of the free parameters. This paper focuses on input-and-state observability, i.e., the property that both initial state and unknown input can be reconstructed from the outputs. First, a simpler statement is presented of a known characterization of generic input-and-state observability. Then, a novel characterization is given of generic left-invertibility with delay one, where the input can be reconstructed up to a single time-step earlier than the most recent output measurement. All characterizations are in terms of properties of graphs associated with the zero pattern.