Table 1 Observed convergence rates in Figures 3 , 4 , 6 and 7 for uniform and adaptive mesh refining

$\mathbf{\parallel }\mathit{\sigma }\mathbf{-}{\mathit{\sigma }}_{\mathit{\ell }}{\mathbf{\parallel }}_{{\mathit{L}}^{{\mathit{p}}^{\mathit{\prime }}}\mathbf{\left(}\mathbf{\Omega }\mathbf{\right)}}^{\mathit{2}}$

$\mathbf{\parallel }\mathit{u}\mathbf{-}{\mathit{u}}_{\mathbf{\ell }}{\mathbf{\parallel }}_{{\mathit{L}}^{\mathit{2}}\mathbf{\left(}\mathbf{\Omega }\mathbf{\right)}}^{\mathit{2}}$

η _R

η _F

η _L

$\mathbf{\parallel }\mathit{D}\mathbf{(}\mathit{u}\mathbf{-}{\mathit{u}}_{\mathit{\ell }}\mathbf{)}{\mathbf{\parallel }}_{{\mathit{L}}^{\mathit{2}}\mathbf{\left(}\mathbf{\Omega }\mathbf{\right)}}^{\mathit{2}}$

η _H

unstab.

stab.

unstab.

stab.

unstab.

stab.

stab.

unstab.

stab.

stab.