A general maximum principle for progressive optimal control of partially observed mean-field stochastic system with Markov chain

In this paper, we study an optimal control problem of partially observed mean-field type stochastic control system with Markov chain in progressive structure. The control variable is allowed to enter the diffusion term of the state process and the drift term of the observation process. The control domain need not be convex. In our model, the cost functional and the observation are also of mean-field type. By virtue of a special spike variation, the related stochastic maximum principle has been obtained. The stochastic maximum principle in progressive structure is essentially different from the classical case