def METHOD_NAME(self, fields):
    U = fields[0:-1]
    phi = fields[-1]
    phi_o = g.lattice(self.M.F_grid_eo, phi.otype)
    phi_e = g.lattice(self.M.F_grid_eo, phi.otype)
    g.pick_checkerboard(g.odd, phi_o, phi)
    g.pick_checkerboard(g.even, phi_e, phi)
    return [U, phi_e, phi_o]