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Abstract:
In this paper, we show that the piecewise linear finite element
solution $u_{h}$ and the linear interpolation $u_{I}$ have
superclose gradient for tetrahedral meshes, where most elements are
obtained by dividing approximate parallelepiped into six
tetrahedra. We then analyze a post-processing gradient recovery
scheme, showing that the global $L^2$ projection of $\nabla u_h$ is
a superconvergent gradient approximation to $\nabla u$.