Quasi Norm a Posteriori Error Estimates Based on Gradient Recovery or Residual Estimation

In this paper, we first derive a posteriori error estimators of residual type for the

and efficient up to higher order terms. We then construct some a posteriori error

posteriori error estimators. It is found that there exist some relationships between

Laplacian. It is shown that the a posteriori error estimators based on gradient

solution is sufficiently smooth and mesh is uniform. Under stronger conditions,

operator, and then some of the gradient recovery based estimates are further

Numerical results demonstrating these a posteriori estimates are also presented.