Wang , Jianye and Ma , Rui. (2018). Unified a Priori Error Estimate and a Posteriori Error Estimate of CIP-FEM for Elliptic Equations.
            <i>Advances in Applied Mathematics and Mechanics</i>. <i>8</i> (4).
            517-535.
         doi:10.4208/aamm.2014.m834