Yanping Chen & Tianliang Hou. (2020). Error Estimates and Superconvergence of RT0 Mixed Methods for a Class of Semilinear Elliptic Optimal Control Problems.
            <i>Numerical Mathematics: Theory, Methods and Applications</i>. <i>6</i> (4).
            637-656.
         doi:10.4208/nmtma.2013.1230nm