The ultraconvergence of derivative for bicubic finite element Original Research Article

It is for the first time that we obtained the image convergence of the derivatives for bicubic finite element by a new recovery technique proposed in Meng and Zhu [L.X. Meng, Q.D. Zhu, The ultraconvergence derivative recovery technique for odd-degree elements – a computer-based test result, Natur. Sci. J. 25 (2) (2003) 117–121]. This numerical postprocessing result is theoretically justified by using projection interpolant and the theory of discrete Green’s function in this paper.