Nesterov acceleration-based iterative method for backward problem of distributed-order time-fractional diffusion equation

This paper is concerned with the inverse problem of determining the initial value of the distributed-order time-fractional diffusion equation from the final time observation data, which arises in some ultra-slow diffusion phenomena in applied areas. Since the problem is ill-posed, we propose an iterated regularization method based on the Nesterov acceleration strategy to deal with it. Convergence rates for the regularized approximation solution are given under both the a priori and a posteriori regularization parameter choice rules. It is shown that the proposed method can always yield the order optimal convergence rates as long as the iteration parameter which appears in the Nesterov acceleration strategy is chosen large enough. In numerical aspect, the main advantage of the proposed method lies in its simplicity. Specifically, due to the Nesterov acceleration strategy, only a few number of iteration steps are required to obtain the approximation solution, and at each iteration step, we only need to numerically solve the standard initial-boundary value problem for the distributed-order time-fractional diffusion equation. Some numerical examples including one-dimensional and two-dimensional cases are presented to illustrate the validity and effectiveness of the proposed method.