Assign and mixed space

[cjham]

Hello,

I am trying to solve a nonlinear problem which has two scalar variables. I have set up a mixed function space
V = FunctionSpace(mesh, "CG", 1)
W = V * V

psi, alpha = Function(W)
u, v = TestFunction(W)

I need to assign an initial condition
ic = Function(W)
ic = Constant(0.0)

psi.assign(ic)
alpha.assign(ic)

But I get an error: 'Indexed' object has no attribute 'assign'. Please can you help?

[Ig-dolci]

Try with

psi = Function(W).sub(0)
alpha = Function(W).sub(1)

[JHopeCollins]

With this approach, psi and alpha would be from different Functions so you wouldn't be able to solve for the whole mixed function in one solve.

[JHopeCollins]

You'll need to give a name to the whole Function, then assign to each subfunction separately:

w = Function(W)
psi, alpha = w.subfunctions
psi.assign(...)
alpha.assign(...)