Discontinuous Galerkin methods for nonlinear scalar hyperbolic conservation laws: divided difference estimates and accuracy enhancement.

In this paper, an analysis of the accuracy-enhancement for the discontinuous Galerkin (DG) method applied to one-dimensional scalar nonlinear hyperbolic conservation laws is carried out. This requires analyzing the divided difference of the errors for the DG solution. We therefore first prove that the [Formula: see text]-th order [Formula: see text] divided difference of the DG error in the [Formula: see text] norm is of order [Formula: see text] when upwind fluxes are used, under the condition that [Formula: see text] possesses a uniform positive lower bound. By the duality argument, we then derive superconvergence results of order [Formula: see text] in the negative-order norm, demonstrating that it is possible to extend the Smoothness-Increasing Accuracy-Conserving filter to nonlinear conservation laws to obtain at least [Formula: see text]th order superconvergence for post-processed solutions. As a by-product, for variable coefficient hyperbolic equations, we provide an explicit proof for optimal convergence results of order [Formula: see text] in the [Formula: see text] norm for the divided differences of DG errors and thus [Formula: see text]th order superconvergence in negative-order norm holds. Numerical experiments are given that confirm the theoretical results.