Two-grid $H^1$-Galerkin mixed finite elements combined with $L1$ scheme for nonlinear time fractional parabolic equations

In this paper, we propose a two-grid algorithm for nonlinear time fractional parabolic equations by $H^1$-Galerkin mixed finite element discreitzation. First, we use linear finite elements and Raviart-Thomas mixed finite elements for spatial discretization, and $L1$ scheme on graded mesh for temporal discretization to construct a fully discrete approximation scheme. Second, we derive the stability and error estimates of the discrete scheme. Third, we present a two-grid method to linearize the nonlinear system and discuss its stability and convergence. Finally, we confirm our theoretical results by some numerical examples.