Christian Klingenberg, Frank Pörner and Yinhua Xia. (2018). An Efficient Implementation of the Divergence Free Constraint in a Discontinuous Galerkin Method for Magnetohydrodynamics on Unstructured Meshes.
            <i>Communications in Computational Physics</i>. <i>21</i> (2).
            423-442.
         doi:10.4208/cicp.180515.230616a