On the quadratic controllability and quadratic feedback minimality

Very recently, the quadratic controllability and quadratic feedback minimality of unstructured norm bounded uncertain linear systems have been studied in a previous paper with explicitly verifiable necessary and sufficient solvability conditions in terms of the so-called “essential subsystem.” In this note, we give the geometric interpretation of the main results in that previous paper, using the strongly controllable subspace and, hence, provide a deeper understanding of the concept of “essential subsystem” in an earlier work.