Unified Approach to the Problem of Full Decoupling via Output Feedback

The article under discussion studies the unmeasurable disturbance decoupling problem (DDP) via the dynamic output feedback from a unified viewpoint for continuousand discrete-time nonlinear control systems as well as for discrete event systems. This is a challenging problem, not having today a complete solution, that is the necessary and sufficient solvability conditions together with the constructive algorithm to compute the feedback law. In [1]1 the intrinsic coordinate-free necessary solvability conditions were obtained in terms of the maximal conditioned invariant subspace and the smallest controlled invariant subspace. The article under discussion provides the sufficient algorithm-based solvability conditions. Unfortunately it does not provide the explicit algorithm for problem solution; the steps of the algorithm are scattered implicitly in the different parts of the article, partly presented in the unified manner, partly treated separately for the continuous and discrete cases. Note that there exist certain differences in the problem statement aswell as in the assumptionsmade on the control system, not to mention the mathematical tools used in [1] and in the article under discussion. Wewill comment these differences below. First, in [1] only analytic state affine systems are considered whereas the article under discussion allows the systems nonlinear in control, and the functions in system