minimum time problem

[YangBo17]

I can't find the minimum time example problem in this repo, could you tell me or provide a minimum time trajectory optimization example.

I have read the article of altro: a time-penalized problem is formulated by modifying the dynamics by adding time step as new state.

However, when I try to formulate such problem, the new state $\tau_k$ always equals to the $\tau_0$ in initial state $x_0$.