ccontrg - central H-infinity controller
returns a realization K of the central controller for the general standard problem in state-space form.
Note that gamma must be > gopt (ouput of gamitg)
P contains the parameters of plant realization (A,B,C,D) (syslin list) with
B = ( B1 , B2 ) , C= ( C1 ) , D = ( D11 D12) ( C2 ) ( D21 D22)
r(1) and r(2) are the dimensions of D22 (rows x columns)