Discontinuous Galerkin methods Advection Galerkin methods A posteriori estimator Advection diffusion equation Advection-diffusion equations Advection-dominated problems Approximation spaces Block solvers Discontinuous galerkin Domain decomposition methods Elliptic problem Error estimates Exponentially fitted schemes Linear systems M -matrix property Numerical tests Perturbation techniques Second orders Singularly perturbed problem advection-diffusion equations discontinuous Galerkin methods exponentially fitted schemes