Fang Fang, Qi Hong & Jiming Wu. (2019). Analysis of a Special $Q_1$-Finite Volume Element Scheme for Anisotropic Diffusion Problems.
            <i>Numerical Mathematics: Theory, Methods and Applications</i>. <i>12</i> (4).
            1141-1167.
         doi:10.4208/nmtma.OA-2018-0080