balreal — balanced realization
[slb [,U] ] = balreal(sl)
Balanced realization of linear system sl=[A,B,C,D]. sl
can be a continuous-time or discrete-time state-space system.
sl is assumed stable.
slb=[inv(U)*A*U ,inv(U)*B , C*U , D]
is the balanced realization.
slb is returned as a syslin list.