A posteriori estimation of the error in the error estimate

In this paper we address the problem of a posteriori estimation of the erro r in the error estimate. We consider the case of estimates for the error in the derivatives, the strains, or the stresses, which are constructed in te rms of locally-computed element error indicators of the element residual, o r the least-squares recovery type. The estimates of the error in the error estimate have the same structure as the original error estimates, and are d etermined by locally averaging (recycling) the original error indicators. T he most accurate indicators of the error in the error indicators are obtain ed by employing a 'harmonic' basis in the recycling of the indicators, name ly, a basis which locally satisfies the partial differential equation and t he boundary conditions. (C) 1999 Elsevier Science S.A. All rights reserved.