The function RARL2.m can be used to reduce the 2-input, 12-states, 2-output model ofan automobile gas turbine studied in many references:
Y.S. Hung and A.G.J. MacFarlane, Multivariable feedback: a quasi-classical approach, Lect. Notes in Control Sci. 40, Springer-Verlag (1982).
K. Glover, All optimal Hankel-norm approximations of linear multivariable systems and their error bounds, Int. J. Control 39, 1115-1193 (1984).
W.-Y. Yan and J. Lam, An approximate approach to H2 optimal model reduction, IEEE Trans. Autom. Control 44, No.7, 1341-1358 (1999).
The results are shown on the Nyquist diagrams of the discrete-time associated system (in blue). According to the theory, a very good approximant is obtained at order 8.