Basis for the Quadratic Nonconforming Triangular Element of Fortin and Soulie

Abstract

A basis for the quadratic ($P_2$) nonconforming element of Fortin and Soulie on triangles is introduced. The local and global interpolation operators are defined. Error estimates of optimal order are derived in both broken energy and $L^2(\Omega)$-norms for second-order elliptic problems. Brief numerical results are also shown.