Further results on ultraconvergence derivative recovery for odd-order rectangular finite elements
For rectangular finite element, the authors give a superconvergence method by SPR technique based on the generalization of a new ultraconvergence record and the sharp Green function estimates, by which they prove that the derivative has ultra-convergence of order \(O(h ^{k+3})\) (\(k \geqslant 3\) being odd) and displacement has order of \(O(h ^{k+4})\) (\(k \geqslant 4\) being even) at the locally symmetry points.
scientific article; zbMATH DE number 5643471