You are right. I only need values or grad values at the quadrature points.
Thanks a lot.
--Junchao Zhang
On Fri, Jul 22, 2016 at 6:52 PM, Wolfgang Bangerth <bange...@tamu.edu>
wrote:
> On 07/22/2016 05:10 PM, Junchao Zhang wrote:
>
>> In matrix assembly, I need to access solution values of the previous
>> time-step at DoFs of the current cell. Is my following code correct? I
>> could
>> not find an example. Thanks.
>>
>> std::vector<types::global_dof_index> local_dof_indices (dofs_per_cell);
>> ...
>> for(; cell!=endc; ++cell) {
>> if (cell->is_locally_owned()) {
>> cell->get_dof_indices (local_dof_indices);
>> fe_values.reinit (cell);
>> ... += old_locally_relevant_solution(local_dof_indices[i]);
>> }
>> }
>>
>
> No. You typically need to access the old solution at *quadrature points*,
> not at the node points. You can find how this is typically done in many
> tutorial programs, e.g., in steps 21, 26, 15. To evaluate a solution at the
> quadrature points, you'll have to do something like
> fe_values.get_function_values (old_solution,
> old_solution_values);
>
> Best
> W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: bange...@math.tamu.edu
> www: http://www.math.tamu.edu/~bangerth/
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