Observe that in this example, the user link cost functions are non-separable and asymmetric
and, hence, the equilibrium conditions (30) cannot be reformulated as the solution
to an optimization problem, but, rather, as the solution to the variational inequalities (31)
(or (32)), or (33) (or (34)). Hoever, given the simplicity of the network and cost structure
in this simple example, we can solve the equilibrium conditions (30) directly.