sfact discrete time spectral factorization F=sfact(P) P real polynomial matrix Finds F, a spectral factor of P. P is a polynomial matrix such that each root of P has a mirror image w.r.t the unit circle. Problem is singular if a root is on the unit circle. sfact(P) returns a polynomial matrix F(z) which is antistable and such that P = F(z)* F(1/z) *z^n For scalar polynomials a specific algorithm is implemented. Algorithms are adapted from Kucera's book. gtild fspecg