Rank conditions for the dynamic disturbance decoupling problem

Considers the dynamic disturbance decoupling problem-DDDP. The authors provide necessary and sufficient rank conditions to solve various versions of the DDDP. The authors establish that when the DDDP is solvable by a "general" dynamic state feedback then it is also solvable by quasi-static state feedback. Furthermore, the authors make a high level examination of the known results, comparing most of the already published material on the DDDP and furnishing elements for a deeper understanding of this matter. >