A posteriori error estimates for stationary slow flows of power-law fluids

We consider the stationary Stokes problem for a class of power-law fluids and prove functional type a posteriori error estimates for the difference of the exact solution and any admissible function from the energy class. We also discuss such error estimates for Bingham-type fluids. The main purpose of such an inequality is to give a directly computable measure of the difference between the exact and an approximate solution. The advantage of functional type a posteriori estimates is that they do not require special properties of the approximate solutions (e.g. Galerkin othogonality) or of the respective finite dimensional spaces used.