Error while integrating backward: Negative path velocity

[yzy244001743]

When this happens, is there any special way to deal with it？

[BryanStuurman]

I added a variable timestep function to my fork:
https://github.com/Taiga-Robotics/trajectories-totg/blob/production/src/Trajectory.cpp#L317
https://github.com/Taiga-Robotics/trajectories-totg/blob/production/src/Trajectory.cpp#L426

moveit also did something special in the same functions which I don't fully understand but also may harden the algorithm against this issue (I've never seen negative path velocity errors with moveit)
https://github.com/moveit/moveit/blob/master/moveit_core/trajectory_processing/src/time_optimal_trajectory_generation.cpp#L532
moveit/moveit#1665

Note that for the two (undocumented and lost) test cases I ran against my patch it was sufficient to fix the issue in the forward integration and the negative integration issue never popped up after that. I put the variable dt into the negative path anyways.