A fast discontinuous finite element discretization for the space-time fractional diffusion-wave equation

In this article, we study fast discontinuous Galerkin finite element methods to solve a space-time fractional diffusion-wave equation. We introduce a piecewise-constant discontinuous finite element method for solving this problem and derive optimal error estimates. Importantly, a fast solution technique to accelerate Toeplitz matrix-vector multiplications which arise from discontinuous Galerkin finite element discretization is developed. This fast solution technique is based on fast Fourier transform and it depends on the special structure of coefficient matrices. In each temporal step, it helps to reduce the computational work from O(N-3) required by the traditional methods to O(N log(2)N), where N is the size of the coefficient matrices (number of spatial grid points). Moreover, the applicability and accuracy of the method are verified by numerical experiments including both continuous and discontinuous examples to support our theoretical analysis. (c) 2017 Wiley Periodicals, Inc.