We analyze a technique to improve the spatial accuracy, by the single application at the end of the simulation of a local post-processing, for pure Lagrange–Galerkin (PLG) methods applied to evolutionary convection-diffusion (possibly pure convection/diffusion) equations with time-dependent domains. The post-processing technique is based on a simple convolution that extracts the ‘hidden accuracy’ of Galerkin schemes, and it is used and rigorously analyzed in a fully discrete context. We prove that, when applied to the numerical solution of PLG schemes, it improves the spatial accuracy in the -norm from order to at least order ⁠, where is the degree of the polynomials defining the finite element space and any interior region of the computational domain meshed with translation-invariant meshes. For pure convection, a spatial accuracy enhancement in the -norm from order to order is obtained by post-processing the numerical solution of PLG schemes. Numerical tests are presented that confirm these theoretical results.

This is a preprint of the following published document: Marta Benítez, Bernardo Cockburn, Post-processing for spatial accuracy-enhancement of pure Lagrange–Galerkin schemes applied to convection-diffusion equations, IMA Journal of Numerical Analysis (published online 20 October 2020), Volume 42, Issue 1, January 2022, Pages 54–77, https://doi.org/10.1093/imanum/draa076