classical control classical control closed loop. See feedback connection feedback parallel series covariance error error design classical classical Kalman estimator Kalman estimator Kalman estimator LQG regulators robustness root locus root locus discrete-time models control design Kalman estimator discretization error covariance error covariance feedback filtering. See Kalman estimator gain margins Kalman filtering Kalman estimator continuous discrete time-varying LQG (linear quadratic-gaussian) method continuous LQ regulator cost function design design LQ-optimal gain regulator margins, gain and phase model building feedback connection parallel connection series connection parallel connection phase margins regulation robustness root locus design design See also Root Locus Design GUI series connection time-varying Kalman filter zero-order hold (ZOH)