Hi, I am trying to solve the following pde with dirichlet boundary conditions. I defined a as a scalar, which is different in different domains.

But I got an ufl.log.UFLValueError in the step

Fl1 = inner(nabla_grad(u) + Constant((1,0)), k*nabla_grad(v))*dx.

Is anyone know how to fix it? I also copied my code here. Thanks in Advance!

```
mesh = UnitSquareMesh(4, 6)
subdomains = MeshFunction("size_t", mesh, 2)
class Omega_0(SubDomain):
def inside(self, x, on_boundary):
return True if (x[0] + x[1]) <= 1 else False
class Omega_1(SubDomain):
def inside(self, x, on_boundary):
return True if (x[0] + x[1]) > 1 else False
subdomain_0 = Omega_0()
subdomain_1 = Omega_1()
subdomain_0.mark(subdomains, 0)
subdomain_1.mark(subdomains, 1)
V0 = FunctionSpace(mesh,"DG",0)
k = Function(V0)
kvalues = [1.5, 10]
for cell in range(len(subdomains.array())):
subdomain_cell = subdomains.array()[cell]
k.vector()[cell] = kvalues[subdomain_cell]
Ve = FiniteElement('Lagrange', mesh.ufl_cell(), 1)
Re = FiniteElement('Real', mesh.ufl_cell(), 0)
X = FunctionSpace(mesh, MixedElement([Ve, Re]))
tol = 1E-14
class topBottomBoundary(SubDomain):
def inside(self, x, on_boundary):
return on_boundary and abs(x[1]) < tol or abs(x[1] - 1) < tol
class leftrightBoundary(SubDomain):
def inside(self, x, on_boundary):
return on_boundary and abs(x[0]) < tol or abs(x[0] - 1) < tol
bc1 = DirichletBC(X.sub(0), Constant(0), topBottomBoundary())
bc2 = DirichletBC(X.sub(0), Constant(0), leftrightBoundary())
bc = [bc1, bc2]
u = TrialFunctions(X.sub(0).collapse())
v = TestFunctions(X.sub(0).collapse())
Fl1 = inner(nabla_grad(u) + Constant((1,0)), k*nabla_grad(v))*dx
F1 = Fl1
Fl2 = inner(nabla_grad(u) + Constant((0,1)), k*nabla_grad(v))*dx
F2 = Fl2
x = Function(X.sub(0).collapse())
a1 = lhs(F1)
L1 = rhs(F1)
solve(a1 == L1, x, bc)
plot(x)
plt.show()
y = Function(X.sub(0).collapse())
a2 = lhs(F2)
L2 = rhs(F2)
solve(a2 == L2, y, bc)
plot(y)
plt.show()
```