# Suppress or turn off degrees of freedom

Dear all,

How can we set the degrees of freedom to be 0 in a region (similar to a boundary condition)?
or turn off so that this region would not be assembled?

You can remove points from the mesh of course - I think â€śtruncâ€ť is used for 2D meshes.

You can assign a varf to a matrix that i represents the equations to be solved
and put in it whatever you want. For the penalty method search docs for â€śtgvâ€ť
which I think is french but with similar english expansions

I have had a few issues however understanding how the memory works
especially with vector fespaces although the approach seems
to be wisdely used with expected results.

1 Like

I do not understand what you wan:

Defined a problem where the solution will be zero some where
and the some where is a part on the domain.

If it is this , I need the formulation of the problem.

1. How to use Lagrange multiplier method to implement a Dirichlet boundary condition?

2. If we have two connected regions -fluid and solid. Velocity is defined on both regions/meshes, but displacement is only defined on the solid region. Not sure is this legal to put this into to one variation form such as the following (thatâ€™s why my initial idea was define the displacement on the whole region and turn it off on `Thf`)?

``````mesh Th = Ths + Thf;

fespace Vh(Th,P2);
fespace Vhs(Ths,P2);

Vh u, v, uh, vh;
Vhs d, dh;
varf fsi([u,v,d],[uh,vh,dh]) =
int2d(Th)(...u..v..)  + int2d(Ths)(...d...)
``````