Superconvergence analysis of an H1-Galerkin mixed finite element method for two-dimensional multi-term time fractional diffusion equations

In this paper, numerical approximation for two-dimensional (2D) multiterm time fractional diffusion equation is considered. By virtue of properties of bilinear element, Raviart-Thomas element and L1 approximation, an H-1-Galerkin mixed finite element fully discrete approximate scheme is established for 2D multi-term time fractional diffusion equation. And then, unconditionally stable of the approximate scheme is rigourously testified by dealing with fractional derivative skilfully. At the same time, superclose results for the original variable u in H-1-norm and the flux (q) over bar = del u in H(div, Omega)-norm are derived. Furthermore, the global superconvergence results for u in H-1-norm are deduced by the interpolation postprocessing operator. Finally, numerical results demonstrate that the approximate scheme provides a valid and efficient way for solving 2D multi-term time fractional diffusion equation.