Local error estimates of mixed discontinuous Galerkin methods for elliptic problems

In this paper local error estimates for mixed discontinuous Galerkin methods including the local discontinuous Galerkin method for solving second-order elliptic problems are established. Our result shows that the errors of both the vector and scalar solutions of the mixed DG methods in a local subdomain are bounded by the local approximation properties of the finite element spaces plus the errors measured in the negative Sobolev norms in a slightly larger subdomain.