Generating Functions for Special Flows over the 1-Step Countable   Topological Markov Chains
  Let $Y$ be a topological Markov chain with finite leading and follower sets. Special flow over $Y$ whose height function depends on the time zero of elements of $Y$ is constructed. Then a formula for computing the entropy of this flow will be given. As an application, we give a lower estimate for the entropy of a class of geodesic flows on the modular surface. We also give sufficient conditions to guarantee the existence of a measure with maximal entropy. 
Dawoud Ahmadi Dastjerdi, Sanaz Lamei
math.DS