I decided to use DoFTool::map_dofs_to_support_points(), so my code above
will be like this:
DoFTools::map_dofs_to_support_points(MappingQ1<dim>, dof_handler,
std::vector<Point<dim>> all_nodes);
std::vector<double> principle_stress;
principle_stress.resize(dof_handler.n_dofs()); //suppose dofs = no_of_nodes
here.
for (unsigned int i = 0; i != dof_handler.n_dofs(); ++i)
{
Point<dim> p = all_nodes[i];
Quadrature<dim> quad(p);
FEValues<dim> fe_values (fe, quad, |update_gradient);
... ... //compute stress with fe_values.shape_grad(i, q)
principle_stress[i] = ... ...
}
//output stress results
DataOut<dim> data_out;
data_out.attach_dof_handler(dof_handler);
data_out.add_data_vector(principle_stress,"principle stress")
But here I'm not sure whether the ordering of points in the vector
"all_nodes" getting from using DoFTool::map_dofs_to_support_points() is the
same with dof_indices of the dof_handler. If so, there is no problem with
the above code. While if not so, the ordering of nodal stress solution
would also be different from dof_handler, as a result, some stress is
attached to wrong dofs by DataOut.
So which case is correct, could anyone give some explanations?
Great thanks!
Best,
David.
On Sunday, May 22, 2016 at 7:43:38 PM UTC+8, David wrote:
>
> Hi, Daniel:
>
> Thank you for your help. But this seems not to be convenient. I am
> thinking to run my code like the following (psuedocode)
>
> for (i=0; i != number_of_nodes; ++i){
> Point<dim> pi = get_point_from_global_index(i);
> Quadrature quad(pi);
> FEValues<dim> fe_values (fe, quad, |update_gradients);
>
> ... ...//do some computations with fe_values.shape_grad(i, q)
> }
>
> In this way, I can easily run over all the triangulation nodes without
> worrying about worrying about recomputation at some nodes if I instead run
> over each cell.
> But the difficullty here that I can't find a function which can do the
> same job as "get_point_from_global_index(i)", namely give me the point with
> global node index i of the triangulation.
>
> Is there any function in dealii with this functionality?
>
> Great thanks!
>
> Best,
> David
>
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