Necessary and sufficient conditions for mixed H/sub 2/ and H/sub infinity / optimal control

It is shown that D.S. Bernstein and W.M. Hadad's (ibid., vol.34, no.3, p.293, 1989) necessary condition for full-order mixed H/sub 2/ and H/sub infinity / optimal control is also sufficient, and that J.C. Doyle et al.'s (Proc. Amer. Control Conf., p.2065, 1989) sufficient condition for full-order mixed H/sub 2/ and H/sub infinity / optimal control is also necessary. They are duals of one another.<
>