copfac - right coprime factorization
returns a right coprime factorization of G.
G = N*M^-1 where N and M are stable, proper and right coprime. (i.e. [N M] left-invertible with stability)
XT and YT satisfy:
[XT -YT].[M N]' = eye (Bezout identity)
G is assumed stabilizable and detectable.