Assign function from one space into mixed space

[Hasupama]

Hi,
I want to assign the values of a function defined in one space to mixed function space as the example below. The assign function did not work. Which function should I need to use in this case to assign the 'phi1' values to 'phi'?

solver_parameters ={	"pc_factor_mat_solver_type": "mumps",
                          "snes_rtol": 1.e-4,
                          "snes_atol": 1.e-3,  
                     	 "maximum_iterations": 100,
                    		"report": True,
                     	 	"error_on_nonconvergence": True,
                     	 									 }


mesh = Mesh('domain.msh')
x = SpatialCoordinate(mesh)

Space_phi = FunctionSpace(mesh, 'CG', 1)
dphi = TrialFunction(Space_phi)
del_phi = TestFunction(Space_phi)
phi1 = Function(Space_phi)

F_phi = x[0]*(  8.854187E-12*phi1.dx(i)*del_phi.dx(i)  )*dx
bc_list=[]
bc_list.append( DirichletBC(Space_phi.sub(0), 0.0, 12) )
bc_list.append( DirichletBC(Space_phi.sub(0), 20e3, 11) )

problem = NonlinearVariationalProblem(F_phi, phi1, bcs=bc_list,   form_compiler_parameters={"quadrature_degree":2})
solver = NonlinearVariationalSolver(problem)
solver.parameters.update(solver_parameters)
solver.solve()

scalar_lin_space = FunctionSpace(mesh, 'CG', 1)
Space = MixedFunctionSpace([scalar_lin_space,scalar_lin_space])
u = Function(Space)
phi,c = split(u)
phi.assign(phi1)

[dham]

This is the easy to make confusion about what split does. split symbolically indexes the entries of the function, which is what you want if you are going to use the components in a Form. However, to actually do something numerical such as assign you instead need the subfunctions of u:

phi, c = u.subfunctions

[Hasupama]

When I tried with subfunction instead of split it gives the error
AttributeError: 'CoordinatelessFunction' object has no attribute 'subfunctions'

The phi values contribute for the weak form.

Is it ok to use assign function for this case I need to assign values which are in different FunctionSpaces.

[dham]

Here is a minimal example:

mesh = UnitSquareMesh(10, 10)
x = SpatialCoordinate(mesh)

Space_phi = FunctionSpace(mesh, 'CG', 1)
phi1 = Function(Space_phi)

scalar_lin_space = FunctionSpace(mesh, 'CG', 1)
Space = MixedFunctionSpace([scalar_lin_space,scalar_lin_space])
u = Function(Space)
phi,c = u.subfunctions
phi.assign(phi1)

I have verified that this works.

If you then need to use phi in a weak form then you should redefine it using split before you do so.

Assign only works between matching function spaces. If you need to transfer Function data between different function spaces then you either need to interpolate or project.