"Expecting a completed form with domains at this point."

Question

Hello,
(my apologies if this appears twice - I can't seem to find the original post).

In any case, I am solving a simple laplace equation with dirichlet BCs applied to the left/right sides of the mesh.

My antiquated version of dolfin would permit the weak form

form = inner(grad(u)*grad(v)*dx)
a,L=lhs(form),rhs(form)

while the current version fails with 'Expecting a completed form with domains at this point."' unless I include a Neumann condition acting on the boundaries, like

form = inner(grad(u)*grad(v)*dx)
form+= Constant(0.)*v*ds
a,L=lhs(form),rhs(form)

Is there something simple I am missing with either my definition of the boundaries or how the weak form is being defined? My full script is below

Thanks!
Pete

from dolfin import *

# Define Dirichlet boundary (x = 0 or x = 1)
class LeftBoundary(SubDomain):
  def inside(self, x, on_boundary):
    return ( on_boundary and \
      (x[0] < 0.5))

class RightBoundary(SubDomain):
  def inside(self, x, on_boundary):
    return ( on_boundary and \
      (x[0] > 0.5))


# Create mesh and define function space
if 1:
  mesh = UnitCubeMesh(8,8,8)
  V = FunctionSpace(mesh,"CG",1)

  # Initialize mesh function for interior domains
  domains = CellFunction("size_t", mesh)
  domains.set_all(0)

  # Initialize mesh function for boundary domains
  boundaries = FacetFunction("size_t", mesh)
  boundaries.set_all(0)

  # Define boundary condition
  bcs=[]
  leftBoundary = LeftBoundary()
  lMarker = 2
  leftBoundary.mark(boundaries,lMarker)
  bc3 = DirichletBC(V, Constant(1.),boundaries,lMarker)
  bcs.append(bc3)

  rightBoundary = RightBoundary()
  rMarker = 3
  rightBoundary.mark(boundaries,rMarker)
  bc4 = DirichletBC(V, Constant(0.),boundaries,rMarker)
  bcs.append(bc4)


  # Define variational problem
  u = TrialFunction(V)
  v = TestFunction(V)

  # Define measures associated w interior domains and boundaries
  dx = Measure("dx")[domains]
  dxs = dx(domain=mesh,subdomain_data=domains)
  ds = Measure("ds")[boundaries]
  dss = ds(domain=mesh,subdomain_data=boundaries)

  D = Constant(1.)

  form = D*inner(grad(u), grad(v))*dxs
  form+= Constant(0.) * v * dss(lMarker)
  a = lhs(form)
  L = rhs(form)


  # Compute solution
  u = Function(V)
  solve(a == L, u, bcs)

Comments

What version of dolfin do you have? With more or less development version this code works for me.

---

$ dolfin-version
1.4.0

It looks like the current version is 1.5, so maybe the issue is resolved with that version.

Thanks!