Title: Superconvergence for the gradient of finite element approximations by least-squares surface fitting

Authors: Xue--Cheng Tai and Junping Wang

Abstract:
A gradient recovery technique is proposed and analyzed for finite
element solutions which gives gradient approximation of high
order. The procedure is based on the method of least-squares
surface fitting in a finite dimensional space corresponding to a
mesh of ``large'' elements, and is thus very close to the patch
recovery technique of Zienkiewicz and Zhu (ZZ). It is proved that
the recovered gradient has a high order superconvergence  for
appropriately-chosen surface fitting spaces.