coefficient ordering in MixedFunctionSpace

Question

Q = FunctionSpace(mesh,'CG',1)
M = MixedFunctionSpace([Q,Q,Q])
u_mixed = Function(M)
s0 = M.sub(0).dim()

Are u_mixed.vector()[0:s0] the coefficients of the subfunction u_mixed[0]?

Answer 1

You cannot make any assumption as to the ordering of dofs in a Function vector.

Comments

Actually you can but you should not!

Answer 2

u_mixed = interpolate(Constant((1.,2.,3.)), M)
u_mixed.vector().array()

produces output

array([ 1.,  2.,  3.,  1.,  2.,  3.,  1.,  2.,  3.,  1.,  2.,  3.,  1.,
    2.,  3.,  1.,  2.,  3.,  1.,  2.,  3.,  1.,  2.,  3.,  1.,  2.,  3.])

so answer is no.

If you're trying to handle somehow assignment to subfunction then note that the issue is now in progress. Also note that standard way of handling assignment to subfunction is for now projection or interpolation. If you want to fiddle directly with DOFs, use helper functions in M.dofmap().