Fast L2-1 sigma Galerkin FEMs for generalized nonlinear coupled Schrodinger equations with Caputo derivatives

The paper is concerned with the unconditional stability and optimal error estimates of Galerkin finite element methods (FEMs) for a class of generalized nonlinear coupled Schrodinger equations with Caputo-type derivatives. We improve the results in [1] to a higher order temporal scheme by using a type of new Gronwall inequality. By introducing a time-discrete system, the error is separated into two parts: the temporal error and the spatial error. As the result of tau-independent of the spatial error, we obtain the L-infinity-norm boundedness of the fully discrete solutions without any restrictions on the grid ratio. The unconditionally optimal L-2-norm error estimate is then obtained naturally. Furthermore, in order to numerically solve the system with nonsmooth solutions, we construct another Galerkin FEM with nonuniform temporal meshes, and corresponding fast algorithm by using sum-of-exponentials technique is also built. Finally, numerical results are reported to show the accuracy and efficiency of the proposed FEMs and the corresponding fast algorithms. (C) 2021 Elsevier Inc. All rights reserved.