Supercloseness analysis of the nonsymmetric interior penalty Galerkin method for a singularly perturbed problem on Bakhvalov-type mesh

For a singularly perturbed convection diffusion problem, we study the super-closeness of the nonsymmetric interior penalty Galerkin (NIPG) method on a Bakhvalov-type mesh. In this process, a new composite interpolation is designed, which consists of Gaul3 Radau projection outside the layer and Gaul3 Lobatto projection inside the layer. Then by choosing the penalty parameters at different mesh points, we derive the supercloseness of k + 21th order (k >= 1) in an energy norm.(c) 2023 Elsevier Ltd. All rights reserved.