If not stated differently we apply standard multiscale V- or W-cycles or improved multiscale V-cycles together with a complete decomposition of the spaces and . Hence, the coarsest grid consists of one interior grid point only. The approximation of used in our experiments is computed by a forward- and backward-substitution from an incomplete factorization (ILU(0)) of the blocks ().

We start our iterations with a normalized random vector and consider without loss of generality the discrete solution to a zero right hand side on the finest grid [22].

Our measure for the speed of convergence is

i.e. the average error reduction within steps with respect to the discrete -norm [22]. We start to measure after one initial iteration to be free of effects from the starting vector. The stopping criterion is for the norm of the absolute error. If this has not been reached with 30 iterations, the iteration is also stopped.