Third, we compare the bound for index models with the asymptotic variance of weighted average derivative estimators of the index coefficients. We characterize the form of the optimal weight function ...

Zhimin Zhang, Derivative Superconvergent Points in Finite Element Solutions of Harmonic Functions: A Theoretical Justification, Mathematics of Computation, Vol. 71, No. 240 (Oct., 2002), pp. 1421-1430 ...