Constant dirichlet boundary condition

General
1

I am trying to solve a simple 2d Poisson equation with constant Dirichlet boundary conditions (u = 0 on boundaries) but don’t find the correct way to set the bc. If, like the tutorial I choose a varying function there is no issue.
uD = fem.Function(V)
uD.interpolate(lambda x: 1 + x[0]**2 + 2 * x[1]**2)

But how can I make it constant? For example using
u_D = fem.Constant(domain, ScalarType(0))
gives an error.

import ufl
import numpy as np
from mpi4py import MPI
from petsc4py import PETSc
from dolfinx import mesh, fem, io, nls, log, plot
from petsc4py.PETSc import ScalarType

nGrid = 10
domain = mesh.create_unit_square(MPI.COMM_WORLD, nGrid, nGrid)

Vh = fem.FunctionSpace(domain, (“CG”, 1))

dofs_L = fem.locate_dofs_geometrical(Vh, lambda x: np.isclose(x[0], 0)) # where x=0
u_L = fem.Constant(domain, ScalarType(0))
bc_L = fem.dirichletbc(u_L, dofs_L)

2

In the tutorials, there are several examples of constant valued BCs, i.e.
https://jsdokken.com/dolfinx-tutorial/chapter1/membrane_code.html#create-a-dirichlet-boundary-condition-using-geometrical-conditions
https://jsdokken.com/dolfinx-tutorial/chapter2/linearelasticity_code.html#boundary-conditions
https://jsdokken.com/dolfinx-tutorial/chapter2/hyperelasticity.html#hyperelasticity
etc.