If Co=ctrb(A,B) has rank r <= n = SIZE(A,1), then there is a similarity transformation Tc such that Tc = [t1 t2] where t1 is the controllable subspace and t2 is orthogonal to t1
Abar = Tc \\ A * Tc , Bbar = Tc \\ B , Cbar = C * Tc
and the transformed system has the form
|Ac A12| |Bc | Abar = |----------|, Bbar = |---|, Cbar = [Cc |Cnc]. |0 Anc| | 0 |
where (Ac,Bc) is controllable, and Cc(sI-Ac)^(-1)Bc = C(sI-A)^(-1)B. and the system is stabilizable if Anc has no eigenvalues in the right half plane. The last output K is a vector of length n containing the number of controllable states.
Package: control