Measuring distance between systems under bounded power excitation

Suggests a way of measuring distance between two systems under a given bounded power excitation. The measure introduced can be used to bound from above and below the difference in closed loop behaviour of two plants for a specified reference or disturbance spectrum. Given an unknown real plant and its identified model, an upper bound on the distance between the plant and its model as expressed by this measure can be obtained from measurable time domain data. The results are particularly relevant for measuring distance between single input systems