Ultraconvergence of finite element method by Richardson extrapolation for elliptic problems with inhomogeneous boundary conditions.

In this article, Richardson extrapolation technique is employed to investigate the local ultraconvergence properties of Lagrange finite element method using piecewise polynomials of degrees k (k≥2) for the second order elliptic problem with inhomogeneous boundary. A sequence of special graded partition TNs are proposed and a new interpolation operator is introduced to achieve 2k order local ultraconvergence for the displacement and derivative. [ABSTRACT FROM AUTHOR]