Abstract. In this paper we first consider a linear time invariant systems with almost periodic forcing term. We propose a new deterministic quadratic control problem, motivated by Da-Prato. With the help of associated degenerate Riccati equation we study the existence and uniqueness of an almost automorphic solutions.
IntroductionThe study of periodic systems, periodic optimization problems and the existence of almost periodic solutions to quadratic control problems have been quite interesting topic to work for many Mathematicians for e.g. [1, 4, 5, 8, 11] and [14]. In [5], Da-Prato has considered the quadratic control problem for the periodic systems in infinite dimension and showed that optimal control is given by feedback control which involves periodic solution of Riccati equation.In [1], Da-Prato and Ichikawa considered the following systemwhere u ∈ L 2 ap (U ), U and Y are real separable Hilbert spaces, B ∈ L(U, Y ) and f ∈ L 2 ap (Y ). Under the assumptions that the pair (A, B) is stabilizable and (M, A) is detectable, they studied the existence of almost periodic solutions for (1.1) and minimized the cost functional:over the set of all controls u such that (1.1) has an almost periodic mild solution.In this paper we study the same problem as considered in [1], by weakening their hypothesis. The conditions (A, B) stabilizable (M, A) detectable is somehow more demanding, whereas similar results as in [1] can be obtained with the assumption on only one pair that the pair (−A, B) is exactly controllable. We generalize their results [1] for the case of almost automorphic solutions that is we wish to minimize the cost functional considered over the set of all controls such that equation (1.1), with almost automorphic forcing term has an almost automorphic solution.Almost automorphy is the generalization of almost periodicity. The notion of almost automorphic functions were introduced by S. Bochner [2] in relation to some aspects of differential geometry.2000 Mathematics Subject Classification. 34 K06, 34 A12, 37 L05.