On Near-controllability, Nearly-controllable Subspaces, and   Near-controllability Index of a Class of Discrete-time Bilinear Systems: A   Root Locus Approach
  This paper studies near-controllability of a class of discrete-time bilinear systems via a root locus approach. A necessary and sufficient criterion for the systems to be nearly controllable is given. In particular, by using the root locus approach, the control inputs which achieve the state transition for the nearly controllable systems can be computed. Furthermore, for the non-nearly controllable systems, nearly-controllable subspaces are derived and near-controllability index is defined. Accordingly, the controllability properties of such class of discrete-time bilinear systems are fully characterized. Finally, examples are provided to demonstrate the results of the paper. 
Lin Tie
cs.SY