Communications on Applied Mathematics and Computation ›› 2025, Vol. 7 ›› Issue (1): 115-150.doi: 10.1007/s42967-023-00359-6

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The High-Order Variable-Coefficient Explicit-Implicit-Null Method for Diffusion and Dispersion Equations

Meiqi Tan1, Juan Cheng2,3, Chi-Wang Shu4   

  1. 1 Graduate School, China Academy of Engineering Physics, Beijing 100088, China;
    2 Laboratory of Computational Physics, Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;
    3 HEDPS, Center for Applied Physics and Technology, College of Engineering, Peking University, Beijing 100871, China;
    4 Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
  • Received:2023-02-11 Revised:2023-09-18 Accepted:2023-12-06 Online:2025-04-21 Published:2025-04-21

Abstract: For the high-order diffusion and dispersion equations, the general practice of the explicitimplicit-null (EIN) method is to add and subtract an appropriately large linear highest derivative term with a constant coefficient at one side of the equation, and then apply the standard implicit-explicit method to the equivalent equation. We call this approach the constant-coefficient EIN method in this paper and hereafter denote it by “CC-EIN”. To reduce the error in the CC-EIN method, the variable-coefficient explicit-implicit-null (VC-EIN) method, which is obtained by adding and subtracting a linear highest derivative term with a variable coefficient, is proposed and studied in this paper. Coupled with the local discontinuous Galerkin (LDG) spatial discretization, the VC-EIN method is shown to be unconditionally stable and can achieve high order of accuracy for both one-dimensional and twodimensional quasi-linear and nonlinear equations. In addition, although the computational cost slightly increases, the VC-EIN method can obtain more accurate results than the CCEIN method, if the diffusion coefficient or the dispersion coefficient has a few high and narrow bumps and the bumps only account for a small part of the whole computational domain.

Key words: Diffusion equation, Dispersion equation, Stability, Explicit-implicit-null (EIN) time discretization, Local discontinuous Galerkin (LDG) method

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