Re: [Libmesh-users] A node does not have dof attached to it?

[Yuxiang W. <yw...@vi...>]

Ah - thank you for the hint!

Totally my bad. I accidentally put L2_LAGRANGE while the element should
really be LAGRANGE. That makes perfect sense now.

I have attached my main function just in case someone else in the future
may find this reference.

Thank you so much Roy!

Best,
Shawn

// Begin the main program.
int main (int argc, char ** argv) {
// Initialize libMesh.
LibMeshInit init (argc, argv);

Mesh mesh(init.comm(), 3);

MeshTools::Generation::build_square (mesh,
2, 2,
-1., 1.,
-1., 1.,
QUAD4);

mesh.set_spatial_dimension (3);

EquationSystems equation_systems (mesh);

ExplicitSystem & director_system = equation_systems.add_system<ExplicitSystem>
("DirectorSystem");
director_system.add_variable("Vnx", FIRST, LAGRANGE);
director_system.add_variable("Vny", FIRST, L2_LAGRANGE);

equation_systems.init ();


// Use an explicit system to store nodal directors
const unsigned int director_system_id = director_system.number();


for (auto node : mesh.node_ptr_range()) {
std::cout << node->n_comp(director_system_id, 0) << std::endl;
std::cout << node->n_comp(director_system_id, 1) << std::endl;
}

return 0;
}

And the output:

./example-dbg
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0


On Thu, Nov 8, 2018 at 6:13 AM Stogner, Roy H <roy...@ic...>
wrote:

>
> On Thu, 8 Nov 2018, Yuxiang Wang wrote:
>
> > Sorry for the naive question. In short, I have a system with three
> > variables (first order Lagrangian elements). I thought that for each of
> the
> > node in the mesh, it would have a DOF attached to it with n_comp==1.
> > However, when I used the following code snippet to check, the n_comp is
> > actually 0 (not 1).
> >
> > for (auto node : mesh.node_ptr_range())
> >  std::cout << node->n_comp(0, 0) << std::endl;
> >
> > What I was trying to achieve is to iterate through all the nodes, and
> > assign solution values to each variable DOF attached to the node from a
> > Eigen::Vector3d. Then I got the error message about:
> >
> > Assertion `comp < this->n_comp(s,var)' failed.
> > comp = 0
> > this->n_comp(s,var) = 0
> >
> > Any help would be appreciated. Thank you!
>
> Are you on a mesh with only first-order geometric elements?  If not
> then the higher-order nodes (e.g. the mid-edge nodes on a TRI6) will
> have n_comp == 0 for first-order Lagrange variables.
> ---
> Roy
>


-- 
Yuxiang "Shawn" Wang, PhD
yw...@vi...
+1 (434) 284-0836