On the equivalence between state space and frequency response models: A missing link for the study of the robustness problem

The present paper focuses on the robustness problem for systems described in their state space form. It is shown that equivalent frequency response robustness results are linked to robustness problems in state space models in which individual entries of the characteristic state space matrices are perturbed. It is also shown how the state feedback compensation and the output feedback compensation are related to the sensitivity problem.