Function value at the boundary

General
1

Hello. Is it possible to somehow look through the print () function, what is the value of the left and right borders?

2

Again, your question is fairly generic, with very little context and no code to illustrate your use-case.

There are various ways to access the data on a facet of a mesh. For instance by getting the entity_dofs or entity_closure_dofs and use them to access values in a function u, print(u.vector()[dof] for dof in entity_dofs_of_facet).

The easiest way to debug a DirichletBC is visually using bc.apply on a function, see: Boundary conditions on edges or nodes - #6 by dokken

3 
u0 = Expression('exp(t+x[0])', degree=1, t=t)
mesh = IntervalMesh(128, 0, 1)
V = FunctionSpace(mesh, 'CG', 2)


def boundary(x, on_boundary):
    return on_boundary
bc = DirichletBC(V, u0, boundary)

Here is the code, I want to know what is the value on the borders of the grid. How to do it?

4

The easiest way (for meshes more complex than an interval) is to inspect this visually (writing to pvd or xdmf, and using a GUI such as Paraview or Visit), as I already stated in:

otherwise you can use the following:

from dolfin import *
t = 5

u0 = Expression('exp(t+x[0])', degree=1, t=t)
mesh = IntervalMesh(128, 0, 1)
V = FunctionSpace(mesh, 'CG', 2)


def boundary(x, on_boundary):
    return on_boundary
bc = DirichletBC(V, u0, boundary)


u_bc = Function(V)

bc.apply(u_bc.vector())

b_values = bc.get_boundary_values()
x = V.tabulate_dof_coordinates()
for dof, value in b_values.items():
    print(x[dof], value)

returning

mpirun -n 3 python3 mwe3.py 
[ 0.] 148.4131591025766
[ 1.] 403.4287934927351
5

Thank you
/////////////////////////////////////////