I realized the mistake I was making, since all my sub-problems share the
same fe space. I don't need a vector of FESystem or FEValues but just one
object of each object for all my sub-problems.
Best,
Karthi.
On Sun, Jan 17, 2021 at 4:48 PM Karthikeyan Chockalingam <
karthi.chockalin...@gmail.com> wrote:
> Thank you very much for your response.
>
>
> Now, I understand since the fe space is the same for the sub-problems I
> can use the same dof_handler for both.
>
>
> Question (1) Does it mean when I distribute the dofs, I should do it twice
> with the same dof_handler?
>
>
> dof_handler.distribute_dofs(fe_one);
>
> dof_handler.distribute_dofs(fe_two);
>
>
>
> Question(2) Currently, both the sub-problems solves almost the same pde
> and in
>
> the future the number of subproblems can be more than two.
>
> So I am planning to define a vector of FESystem<dim>.
>
>
> std::vector<FESystem<dim>> fe;
>
>
> In the body of the constructor I have
>
>
> for(unsigned int i=0; i < num_index; i++)
>
> fe.push_back({FE_Q<dim>(degree),1,FE_Q<dim>(degree)});
>
>
> The above code compiles.
>
>
> Likewise define a vector for system_matrix, solution, old_solution,
> system_rhs.
>
> Is this the approach correct?
>
>
> Question (3)
>
>
> Can I do the same for FEValues?
>
>
> std::vector<FEValues<dim>> fe_vector_values;
>
>
> for(unsigned int i=0; i < num_index; i++)
>
> fe_vector_values.push_back({fe_vector[i], quadrature_formula,
> update_values});
>
>
> Strangely enough depending on where the above code is located,
>
> it sometimes gives me compile errors.
>
>
> If there is a better approach please let me know. Thank you!!
>
>
> Best,
>
> Karthi.
>
> On Sat, Jan 16, 2021 at 5:22 PM Wolfgang Bangerth <bange...@colostate.edu>
> wrote:
>
>> On 1/14/21 10:51 AM, Karthi wrote:
>> > I have gone through a lot of tutorials. I would like to understand the
>> basic
>> > relation between dof_handler and FESystem. I am trying to solve
>> _two_ 4th
>> > order equations on the same mesh (or triangulation). And each equation
>> is
>> > split into two second order equations.
>> >
>> > FESystem<dim> fe_one, fe_two;
>> >
>> > BlockSparseMatrix<double> system_matrix_one, system_matrix_two;
>> >
>> > BlockVector<double> solution_one, solution_two;
>> >
>> > BlockVector<double> old_solution_one, old_solution_two;
>> >
>> > BlockVector<double> system_rhs_one, system_rhs_two;
>> >
>> > Question (1) Do I need one or two dof_handler?
>> >
>> > DoFHandler<dim> dof_handler;
>> >
>> > Where,
>> >
>> > fe_one(FE_Q<dim>(degree),1, FE_Q<dim>(degree),1)
>> >
>> > fe_two(FE_Q<dim>(degree),1, FE_Q<dim>(degree),1)
>> >
>> > Some additional information, both the fe_one and fe_two systems are
>> > _independently solved_ in a semi-implicitly manner. Meaning
>> system_matrix_one
>> > is a function of old_solution_one and old_solution_two, likewise for
>> > system_matrix_two.
>>
>> No. A DoFHandler in essence just describes a function space: The
>> triangulation
>> provides the subdivision of the domain into cells, the finite element
>> provides
>> information about what the polynomial space is, and the DoFHandler
>> provides an
>> enumeration of degrees of freedom. As a consequence, if you want to use
>> the
>> same function space for your two problems, then you can use the same
>> DoFHandler for both of your sub-problems.
>>
>>
>> > Question (2) I am assuming one block spartisty_pattern is enough and
>> use the
>> > same for both the system_matrix?
>> >
>> > BlockSparsityPattern sparsity_pattern;
>>
>> Correct.
>>
>> Best
>> W.
>> --
>> ------------------------------------------------------------------------
>> Wolfgang Bangerth email: bange...@colostate.edu
>> www: http://www.math.colostate.edu/~bangerth/
>>
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