name 'homogenize' is not defined

Question

Hi, I am running FEniCS 2016.1 and the homogenize funcion is not recognized.
https://fenicsproject.org/documentation/dolfin/1.5.0/python/programmers-reference/fem/bcs/homogenize.html

For example, with:

from dolfin import *
mesh = UnitSquareMesh(4, 4)
V = FunctionSpace(mesh, 'Lagrange', 1)
u0 = Expression('1 + x[0]*x[0] + 2*x[1]*x[1]')
def u0_boundary(x, on_boundary):
    return on_boundary

bc = DirichletBC(V, u0, u0_boundary)
bc0 = homogenize(bc)

I get the following error:
bc0 = homogenize(bc)
NameError: name 'homogenize' is not defined

What is wrong? Any help would be appreciate.

Comments

Hi, homogenize is now a member function of DirichletBC class. See e.g. the last point in release notes version 1.6.0

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Ok, i have seen it, thx.
Then, the correct syntax is now

bc0 = bc.homogenize()

Besides, the documentation is

homogenize()
Set value to 0.0

So, is this equivalent to

bc0 = DirichletBC(V, 0, u0_boundary)

I am not sure to understand what does exactly the function.

---

You understand it correctly.

---

Well, then what is the interest of the function homogenize, if it only means set the dirichlet value to 0?
There should be a deeper reason for the fonction homogenize to exist, no?

Besides, the outcome of two syntax are not identical:

from dolfin import *
mesh = UnitSquareMesh(4, 4)
V = FunctionSpace(mesh, 'Lagrange', 1)
u0 = Expression('1 + x[0]*x[0] + 2*x[1]*x[1]')
def u0_boundary(x, on_boundary):
    return on_boundary

bc = DirichletBC(V, u0, u0_boundary)

bc = bc.homogenize()
# or
bc = DirichletBC(V, 0, u0_boundary)

u = TrialFunction(V)
v = TestFunction(V)
f = Constant(0)
a = inner(nabla_grad(u), nabla_grad(v))*dx
L = f*v*dx
Compute solution
u = Function(V)
solve(a == L, u, bc)

is working for both syntax

But:

M = assemble(a)
bc.apply(M)

I get the following error with bc = bc.homogenize()

AttributeError: 'NoneType' object has no attribute 'apply

and no error with bc = DirichletBC(V, 0, u0_boundary)

Then, there is a difference somewhere.
And how can i use the function apply with a BC defined with homogenize?

Answer 1

To answer the questions from your comments, consider

from dolfin import *

mesh = UnitSquareMesh(10, 10)
V = FunctionSpace(mesh, 'CG', 1)
u = TrialFunction(V)
v = TestFunction(V)
a = inner(grad(u), grad(v))*dx
A = PETScMatrix(); assemble(a, A)
A_h = PETScMatrix(); assemble(a, A_h)

bc = DirichletBC(V, Constant(0), 'on_boundary')
bc_h = DirichletBC(V, Constant(1), 'on_boundary')
foo = bc_h.homogenize()      # Now bc_h acts like bc
print type(foo)              # Not DirichletBC but none!

bc.apply(A)
print '|A|', A.norm('linf')
bc_h.apply(A_h)
print '|A_h|', A_h.norm('linf')
# Show they are same
A -= A_h
print '|A-A_h|', A.norm('linf')