def eqS((A, B, C, D), (An, Bn, Cn, Dn)):
    A = mt(A); B = mt(B); C = mt(C); D = mt(D)
    An = mt(An); Bn = mt(Bn); Cn = mt(Cn); Dn = mt(Dn)
    b = B[:, 0]
    bn = Bn[:, 0]
    n = len(A)
    Sy = b
    Sny = bn
    for i in range(1, n):
        Apow = copy(A)
        Anpow = copy(An)
        if not i == 1:
            for j in range(i-1):
                Apow = dot(Apow, A)
                Anpow = dot(Anpow, An)
        Sy = hstack((Sy, dot(Apow, b)))
        Sny = hstack((Sny, dot(Anpow, bn)))
    return dot(Sy, inv(Sny))