AN A POSTERIORI ERROR ESTIMATE OF THE OUTER NORMAL DERIVATIVE USING DUAL WEIGHTS ̊

We derive a residual based a-posteriori error estimate for the outer normal derivative of approximations to Poisson's problem. By analyzing the solution of the adjoint problem, we show that error indicators in the bulk may be defined to be of higher order than those close to the boundary, which lead to more economic meshes. The theory is illustrated with some numerical examples.

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