How to calculate reducing velocity

Hello everybody, I have a small question:

I have a matrix: A(2099x2)

A(:,1) is the time in seconds and A(:,2) is a trajectory velocity (walking). I have a person who walks a certain distance ‘trajectory’ this person has to direct himself to specific targets while he walks he slows down (‘‘label stop’’). I want to know how to calculate this ‘’stops’’. The ‘stops’ are not really stops but reducing velocity during the trajectory.

Thanks very much!