Float navier_stokes_dg::space_norm (const value_type& xh) const {
  return sqrt (mu(xh[0],xh[0]) + mp(xh[1],xh[1]));
}
Float navier_stokes_dg::dual_space_norm (const value_type& mrh) const {
  value_type rh(2);
  rh[0] = field (Xh,0);
  rh[1] = field (Qh,0);
  rh[0].set_u() = smu.solve(mrh[0].u());
  rh[1].set_u() = smp.solve(mrh[1].u());
  return sqrt (dual(rh[0],mrh[0]) + dual(rh[1],mrh[1]));
}
