BUG: Cofunction.sub() assignment of a base form is not working about firedrake

[Ig-dolci]

The issue arises from the assemble of a form in a Mixed Function Space. Consider the code:

from firedrake import *

mesh = UnitSquareMesh(2, 2)

BDM = FunctionSpace(mesh, "BDM", 1)
DG = FunctionSpace(mesh, "DG", 0)

# Create a Mixed Function Space 
W = BDM * DG

# Define test and trial functions for DG
v0 = TestFunction(DG)
sigma, u = TrialFunctions(W)
tau, v = TestFunctions(W)

# Assemble the form
aux = assemble(Constant(1.0) * v * dx)

aux = assemble(Constant(1.0) * v * dx) is returning a Cofunction in the Mixed Function Space BDM x DG. Therefore, when we try:

c = Cofunction(W.dual())
c.sub(1).assign(aux)

This assignment fails because the function spaces of aux and c.sub(1) do not match, i.e., aux.function_space() != c.sub(1).function_space().

[Ig-dolci]

That is not a bug. I was just doing the math wrong assignment.