On the determination of the order and the degree of a zero of a rational matrix
Joos P. L. Vandewalle, P. Dewilde · IEEE Transactions on Automatic Control · 1974
A simple formula for the order and the degree of a zero of a multivariable system at a point p0of the complex plane is deduced using the Laurent expansion of the transfer function at the point p0The formula avoids the need for computing the inverse or generalized inverse of the matrix, and allows easy determination of factorable elementary factors.