split/combine functions from/to MixedFunctionSpace

Question

Now that bugs #193 and #119 are resolved (https://bitbucket.org/fenics-project/dolfin/issue/193/improve-the-procedure-of-identifying, https://bitbucket.org/fenics-project/dolfin/issue/119), is it actually possible

• ...to combine two functions u (from function space W) and p (from P) to a function up (from `MixedFunctionSpace([W, P])?
• ...to split a function up from MixedFunctionSpace([W, P]) into functions u and p from W and P, respectively?

I suppose the FunctionAssigner will be somehow involved in either of the steps. Is there example code for this?

Answer 1

This post provides an example of how to split from MixedFunctionSpace:

http://fenicsproject.org/qa/4081/mixedfunctionspace-update-a-subfunction