A High-Order Difference Scheme for the Space and Time Fractional Bloch-Torrey Equation.

In this paper, a high-order difference scheme is proposed for an one-dimensional space and time fractional Bloch-Torrey equation. A third-order accurate formula, based on the weighted and shifted Grunwald-Letnikov difference operators, is used to approximate the Caputo fractional derivative in temporal direction. For the discretization of the spatial Riesz fractional derivative, we approximate the weighed values of the Riesz fractional derivative at three points by the fractional central difference operator. The unique solvability, unconditional stability and convergence of the scheme are rigorously proved by the discrete energy method. The convergence order is 3 in time and 4 in space in L-1(L-2)-norm. Two numerical examples are implemented to testify the accuracy of the numerical solution and the efficiency of the difference scheme.