Unitary Matrix Models with a topological term and discrete time Toda   equation
  We study the full unitary matrix models. Introducing a new term $l log U$, l plays the role of the discrete time. On the other hand, the full unitary matrix model contains a topological term. In the continuous limit it gives rise to a phase transition at $\theta=\pi$. The ground state is characterize by the discrete time l. The discrete time l plays like the instanton number. 
Masato Hisakado