[1] V. M. Popov: 
Invariant description of linear time-invariant controllable systems. SIAM J. Control 10 (1972), 252-264. 
MR 0479501 | 
Zbl 0251.93014[2] R. E. Kalman: 
Kronecker invariants and feedback. In: Ordinary Differential Equations (L. Weiss, ed.), Academic Press, New York 1972, pp. 459-471. 
MR 0421751 | 
Zbl 0308.93008[3] F. R. Gantmacher: 
Theory of Matrices. Chelsea, New York 1959. 
Zbl 0085.01001[4] J. Rissanen: 
Basis of invariants and canonical forms for linear dynamical systems. Automatica 70 (1974), 175-182. 
MR 0484602[5] M. S. Caroli, R. P. Guidorzi: Algebraical links between multicompanion structures. Ricerche di Automatica 4 (1973), 1-17.
[6] W. A. Wolovich: 
Linear Multivariable Systems. Springer-Verlag, Berlin--Heidelberg--New York 1974. 
MR 0359881 | 
Zbl 0291.93002[7] S. Beghelli, R. P. Guidorzi: 
A new input-output canonical form for multivariable systems. IEEE Trans. Automat. Control AC-21 (1976), 692-696. 
MR 0416675 | 
Zbl 0332.93018[8] R. P. Guidorzi, S. Beghelli: 
Input-output multistructural models in multivariable systems identification. In: Preprints of the 6th IFAC Symp. on Identification and System Parameter Estimation, Washington D. C., 1982, pp. 461-465. 
MR 0795333