On Wed, 11 Apr 2018, 서승진 wrote:

1) In visualization, I used paraview and open out_2.e (in introduction_ex4).

The paraview displayed the white box. I think that this is mesh for the example.

However, paraview didn't displayed the solution distribution (colored box).

Is the problem is come from the absence of post-processing in the example?

Did you tell paraview to display the solution distribution?

When I first open out_2.e in paraview 5.0.1, it displays nothing.

When I then click on the Properties->Variables->u checkbox and hit
Apply, it displays a white box (the domain for the example).

When I then change from "vtkBlockColors" to "u" in the active variable
controls toolbar, it displays a box colored by the solution.

I understood that Libmesh examples use Dirichlet condition, and the part to set 
boundary condition is;

std::set<boundary_id_type> boundary_ids;
boundary_ids.insert(0);
boundary_ids.insert(1);
boundary_ids.insert(2);
boundary_ids.insert(3);
DirichletBoundary dirichlet_bc(boundary_ids, variables, exact_solution_object);
system.get_dof_map().add_dirichlet_boundary(dirichlet_bc);

However, I couldn't find the part to set the initial value of u_var and value 
of boundary condition for each boundary.ids...

How I can set the value of initial condition and boundary conditions?

"exact_solution_object" in the above code is the functor which returns
boundary condition values.

Initial condition values are typically set with
System::project_solution().  See transient_ex1.C for an example.
  
3) In mailing list, some people mentioned about the example which
contain Neumann boundary condition with penalty method,

This sounds confused.  The penalty method sets a Robin boundary
condition which is closely related to a desired Dirichlet boundary
condition, it's not for Neumann boundary conditions.

so I've searched the example in Libmesh, but I couldn't find. Is
there no neumann B.C. example in Libmesh?

systems_of_equations_ex2.C, if you modify it to use the
set_stagnation_bcs() function, has a homogeneous Neumann outflow
condition. fem_system_ex4.C has a homogeneous Neumann condition on one
side.

But homogeneous Neumann in most finite element formulations means "do
nothing", so if you have a heterogeneous Neumann boundary you probably
still want an example... let's see.

miscellaneous_ex9.C uses a constant Neumann flux = 1 on one domain side.

systems_of_equations_ex4.C (and _ex5.C, and _ex6.C...) use a constant
Neumann traction on one side.

Thanks for reading my email.

For your answer, I successfully installed the libmesh.

You're welcome.

You should probably join and send future emails to libmesh-users,
though; that way they might not languish without reply quite as long
when I'm busy.
---
Roy
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