How to manually set boudnary DOFs for H1 grid function

[Guosheng Fu]

Hello again,

I have a H1 gridfunction, say, obtained from interpolation from a DG solution, and would like to manually set the boundary dofs to 0. I don't know how to locate the global indexes of boundary dofs.

The finite element space have pure Dirichlet boundary conditions, and I need vanishing boundary dofs for my grid function, without modifying the internal dofs.

Thanks,
Guosheng

[schruste]

Hi Guosheng,

If I understood you correctly you can do it this way:

for i,freedof in enumerate(V.FreeDofs()):
    if not freedof:
        u.vec[i] = 0.0

The FreeDofs() of an FESpace are all degrees of freedom which are not marked as Dirichlet-Dofs. So whereever you set Dirichlet-boundaries in the space, you will have V.FreeDofs(i) = False.

Alternatively you can loop over all boundary elements (this would be a solution which is independent of what the dirichlet-marking in the FESpace says) and set all boundary dofs to zero:

for el in V.Elements(BND):
    for i in el.dofs:
        u.vec[i] = 0.0

Best,
Christoph

[Guosheng Fu]

Hi Christoph,

Thanks!
That's exactly what I want.

Best,
Guosheng