On the Morgan problem with stability

where the polynomial matrices Ni(s) and D(s) form a normal external description (NED) of (C, A H ) ; see [11]. The matrices N(s) := CNx(s) and D(s) then form, not necessarily coprime, a matrix fraction description (MFD) of (C,A,B). Recall that Ni(s) and D(s) are right coprime with D(s) being column reduced. The column degrees, Cj := degciD(s), i = 1,2,... ,m, are the controllability indices of (C, A, B). We shall further assume (see [8] for more details) that V* = TV, where TV denotes the maximal controllability subspace lying in Ker C and V* is the maximal (A,B)invariant subspace contained in Ker C.