1. GEORGAKIS , C. , and BAUER , R. P. , 1978 ,Proc. IFAC Conf., Helsinki , pp. 2409 – 2413 .
2. Controllability and time-optimal control of systems with slow and fast modes
3. Singular perturbations and order reduction in control theory — An overview
4. LITZ , L. , 1979 ,Reduktion der Ordnung linearer Zustandsraummodelle mittels modaler Verfahren( Stuttgart : Hochschul-Verlag ) 1980 a,Proc. IFAC, Toulouse, Symp. Large Scale Systems, ed. A. Titli, M. G. Singh (New York Pergamon Press), pp. 195-202 ; 1980 b,Proc. Systems Analysis and Simulation, ed. A. Sydow (Berlin Akademie-Verlag) , pp. 230 – 234 .