I put my non-smart solution here in case if there's no easy way of doing it
in deal.II and someone else needs it.
// The vector I want to output is the solution for vector-valued problem.
// I want to output the cell-average value for the 0th component.
Vector<double> modi (solu);
Quadrature<dim> qq(fe.get_unit_support_points());
FEValues<dim> fv(fe, qq, update_values | update_quadrature_points);
std::vector<bool> selected_dofs (dof_handler.n_dofs());
// comp[0] is the 0th component of std::vector<FEValuesExtractors::Scalar>
for the system
DoFTools::extract_dofs(dof_handler, fe.component_mask(comp[0]),
selected_dofs);
std::vector<types::global_dof_index> local_to_global_dof (fe.dofs_per_cell);
// modify the 0th component
for (typename DoFHandler<dim>::active_cell_iterator
cell=dof_handler.begin_active(); cell!=dof_handler.end(); ++cell) {
fv.reinit(cell);
std::vector<double> local_sol(qq.size());
fv[comp[0]].get_function_values(solu_out,local_sol);
double avg = std::accumulate(local_sol.begin(), local_sol.end(), 0.) /
local_sol.size();
cell->get_dof_indices (local_to_global_dof);
for (auto i=0; i<fe.dofs_per_cell; ++i) {
if (selected_dofs[local_to_global_dof[i]]) {
solu_out[local_to_global_dof[i]] = avg;
}
}
}
If anyone has any smarter idea, please let me know and thanks in advance.
Weixiong
在 2018年3月27日星期二 UTC-7下午2:35:37，Weixiong Zheng写道：
>
> Hi
>
> I am trying to output an cell average solution for a code using DG
> bilinear element in 2D. Is there a trivial way to project DG-1 to DG-0? Or
> is there any function I can call to output the solution at some specfic
> points, say the center point of the cell?
>
> Thanks
>
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