A note on diagonal decoupling

Diagonal decoupling problem is considered for a special case where the original system is already diagonal and it is desired to increase the infinite zero orders of the system while keeping it still diagonal. Thus, the problem being considered may also be viewed as an infinite zero assignment problem with the exception that the diagonality is preserved. The necessary and sufficient conditions for solvability of this problem are given and attainable infinite zero orders are characterized in terms of the structural properties of the system. The results are illustrated by an example.