The "place" command could not place the poles at the specified locations. Probable causes include: * (A,B) is nearly uncontrollable * The specified locations are too close to each other.

Am trying for a system which is ustable but not controllable but observable system

Answer 1

[Pan Zhao]

If your system is not controllable, then you cannot place the closed-loop poles at arbitrary positions. Observability (determined by A, C matrices) is not relevant here.