Hi Seven,
Thanks for reporting back that you missed a step in the application of the
constraints! I'm glad that you managed to solve your problem.
Best regards,
Jean-Paul
On Friday, March 24, 2017 at 2:09:35 AM UTC+1, seven wrote:
>
> Guess I figured it out. I didn't do
> constraints.distribute();
>
>
> 在 2017年3月23日星期四 UTC-4上午1:38:32，seven写道：
>>
>>
>> Hello all,
>>
>> I am trying to project a solution in FE_DGP(sol_dg) to FE_Q (sol_cg), but
>> I only know the gradients of sol_dg and its values at some vertices, so I
>> want to fix values of sol_cg at the same vertices after the projection.
>>
>> The first method I tried is quite straightforward, but the resulting
>> global matirx is very ill-conditioned. I set the corresponding row to zero
>> except the diagonal entry, and then change the right hand size.
>>
>> for( ; cell_c!= endc;++cell_dg, ++cell_c ){
>> const unit active_index = cell_dg->active_cell_index();
>> if(interface_flag[active_index] == 1){
>> fe_values_continuous.reinit(cell_c);
>> fe_values_v_dg.reinit(cell_dg);
>> fe_values_v_dg.get_function_values(solution, solu_dg);
>> cell_c->get_dof_indices(local_dof_indices_c);
>> for(unit vert=0; vert<4; ++vert){
>> // local_dof_indices_c[vert] global index
>> const unit index_i = local_dof_indices_c[vert];
>> ls_rhs_continuous(index_i) = solu_dg[vert]* aver_diag;
>> for(unit i=0; i> ls_matrix_continuous.set(local_dof_indices_c[vert], i, 0.);
>> ls_matrix_continuous.set(index_i, index_i, aver_diag);
>> }
>> }
>>
>> }
>> so I want to use constraint matrix to do the same thing, but cannot get
>> the right answer.
>>
>> for( ; cell_c!= endc;++cell_dg, ++cell_c ){
>> const unit active_index = cell_dg->active_cell_index();
>> if(interface_flag[active_index] == 1){
>> fe_values_continuous.reinit(cell_c);
>> fe_values_v_dg.reinit(cell_dg);
>> fe_values_v_dg.get_function_values(solution, solu_dg);
>> cell_c->get_dof_indices(local_dof_indices_c);
>> for(unit vert=0; vert<4; ++vert){
>> // local_dof_indices_c[vert] global index
>> const unit index_i = local_dof_indices_c[vert];
>> constraints.add_line(index_i);
>> constraints.set_inhomogeneity(index_i, solu_dg[vert]);
>> }
>> }
>> }
>> constraints.close();
>>
>> cell_c = dof_handler_continuous.begin_active();
>> cell_dg = dof_handler.begin_active();
>> for( ; cell_c!=endc; ++cell_c, ++cell_dg){
>> fe_values_dg.reinit(cell_dg);
>> fe_values_dg.get_function_gradients(solution, grad_dg);
>>
>> ls_matrix = 0;
>> ls_rhs = 0;
>> fe_values_continuous.reinit(cell_c);
>>
>> for(unit q=0; q> for(unit i=0; i> ls_rhs(i) += fe_values_continuous.shape_grad(i,q)
>> * fe_values_continuous.JxW(q)
>> * grad_dg[q];
>> for(unit j=0; j> ls_matrix(i,j) += fe_values_continuous.shape_grad(i,q)
>>* fe_values_continuous.shape_grad(j,q)
>>* fe_values_continuous.JxW(q);
>> }
>> }
>> cell_c->get_dof_indices(local_dof_indices_c);
>> constraints.distribute_local_to_global (ls_matrix, ls_rhs,
>> local_dof_indices_c,
>> ls_matrix_continuous,
>> ls_rhs_continuous);
>>
>> Any help would be appreciated
>>
>> Thanks,
>> Jiaqi
>>
>
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