// create transfer operators from level i to i+1 (note that this will only work for either uniformly refined grids or adaptive grids with RefinementType=COPY)
auto t = std::make_shared<TransferOperator>();
t->setup(*grid, i, i+1);
transfer[i] = t;
}
auto linearMultigridStep = std::make_shared<Dune::Solvers::MultigridStep<Matrix, Vector> >(