Abstract: | Abstract For the multidimensional ARMA system A(z)y k = C(z)w k it is shown that stability (det A(z) ≠= 0, ∀ z : |z| ≤ 1) of A(z) is equivalent to the trajectory boundedness in the mean square sense (MSS) which, as a rule, is a consequence of a successful stochastic adaptive control leading the closed-loop of an ARMAX system to a steady state ARMA system. In comparison with existing results the stability condition imposed on C(z) is no longer needed. The only structural requirement on the system is that det A(z) and det C(z) have no unstable common factor. Supported by the National Natural Science Foundation of China (No. 60074003) and by the Ministry of Science and Technology of China. |