The aim of this paper is to study the existence of classical solutions to the following fractional integro-differential equation
where stands for the Riemann-Liouville derivative of order , , is the infinitesimal generator of an analytic semigroup in a Banach space is a suitable function, and a Banach space. , which may be interpreted as a control of the system, is defined by and , .
By means of the contraction mapping, the authors prove the existence and uniqueness of a classical solution of the initial value problem associated to (1). Then, they show the existence and uniqueness of an optimal mild solution among all the solutions of (1) which are bounded over . Note that the notion of optimal solution was introduced by G. M. N’Guérékata in [Riv. Mat. Univ. Parma, IV. Ser. 9, 145–151 (1983; Zbl 0547.34049)]. Finally, they study sufficient conditions for the existence and uniqueness of a weighted pseudo-almost periodic classic solution. An example is also given to illustrate the abstract results.