“…The LDG method is a form of finite-element method; it was first proposed as a generalisation of the discontinuous Galerkin (DG) method for a convection-diffusion Symmetry 2021, 13, 2291 2 of 26 problem [12]. Later, it was applied to solve the purely elliptic problem [13], convectiondiffusion problems [14], Stokes system [15], KdV-type equations [16], Hamilton-Jacobi equations [17], time-dependent fourth-order problems [18] and other higher-order partial differential equations [19]. Because the LDG method shares many advantages of the DG methods and can effectively simulate the acute change of a singular solution, it is particularly suited to solving singularly perturbed problems.…”