Averaging principles for time-inhomogeneous multi-scale SDEs via nonautonomous Poisson equations

The purpose of this paper is to establish asymptotic behaviors of time-inhomogeneous multi-scale stochastic differential equations (SDEs). To achieve them, we analyze the evolution system of measures for time-inhomogeneous Markov semigroups, and investigate regular properties of nonautonomous Poisson equations. The strong and the weak averaging principle for time-inhomogeneous multi-scale SDEs, as well as explicit convergence rates, are provided. Specifically, we show the slow component in the multi-scale stochastic system converges strongly or weakly to the solution of an averaged equation, whose coefficients retain the dependence of the scaling parameter. When the coefficients of the fast component exhibit additional asymptotic or time-periodic behaviors, we prove the slow component converges strongly or weakly to the solution of an averaged equation, whose coefficients are independent of the scaling parameter. Finally, two examples are given to indicate the effectiveness of all the averaged equations mentioned above.