Hello,
I found out the solution and wanted to post here in case some one faces
similar problem.
In my case, the right hand side was already assembled and there was no way
that it could be assembled during the calculations as done usually.
Think of it as reading an assembled rhs (without application of
Dirichlet bcs) from a file.
I found out, that if the constraints are homogeneous, I can use
constraints.distribute_local_to_global as described below to assemble this
rhs and apply bcs / constraints at the same time.
std::map<unsigned int, bool> dof_touched;
for (; cell != endc; ++cell)
if (cell->is_locally_owned())
for (unsigned int v = 0; v < GeometryInfo<dim>::
vertices_per_cell; ++v)
for (unsigned int d = 0; d < dim; ++d)
dof_touched[cell->vertex_dof_index(v, d)] = false;
cell = dof_handler.begin_active();
const unsigned int dofs_per_cell = fe.dofs_per_cell;
std::vector<types::global_dof_index> local_dof_indices (dofs_per_cell);
Vector<double> cell_rhs(dofs_per_cell);
for (; cell != endc; ++cell)
if (cell->is_locally_owned())
{
cell_rhs = 0;
cell->get_dof_indices (local_dof_indices);
for (unsigned int i = 0; i < local_dof_indices.size(); ++i)
{
unsigned int dof = local_dof_indices[i];
if (dof_touched[dof] == false && locally_owned_dofs.
is_element(dof))
{
dof_touched[dof] = true;
cell_rhs(i) = assembled_rhs[dof];
}
}
constraints.distribute_local_to_global (cell_rhs,
local_dof_indices,
system_rhs);
}
On Monday, September 12, 2016 at 1:35:52 PM UTC-4, RAJAT ARORA wrote:
>
> Hi Daniel,
>
> Thanks for the reply.
>
> This indeed is one way of doing it.
>
> I was wondering if there is any other way in which this can be done.
>
> Thanks again.
>
>
> On Monday, September 12, 2016 at 5:04:47 AM UTC-4, Daniel Arndt wrote:
>>
>> Rajat,
>>
>> The first equation is the usual equilibrium equation. It is solved to
>>> give displacements. The stiffness matrix is then multiplied by this global
>>> displacement vector to give the global traction vector which forms the rhs
>>> for the second equation.
>>>
>> The easiest solution to deal with constraints to deal with them while
>> assembling the matrix. Therefore, I would not compute the right-hand side
>> for the second equation beforehand.
>> Instead just do it while assembling the second equation and use
>> constraints.distribute_local_to_global().
>>
>> Best,
>> Daniel
>>
>
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