Liping Gao and Dong Liang. (2012). New Energy-Conserved Identities and Super-Convergence of the Symmetric EC-S-FDTD Scheme for Maxwell's Equations in 2D.
            <i>Communications in Computational Physics</i>. <i>11</i> (5).
            1673-1696.
         doi:10.4208/cicp.121110.030611a