+ /*
+ This is where cyclical dependencies are avoided. In beam collision avoidance,
+ beams often need to avoid other beams. To do this, they need to know the beam's
+ position. But, if that second beam needs to know the first beam's position, we
+ have a cyclical dependency. So, we only ever add signaled beams to active_beams_
+ that existed BEFORE this time step. This is controlled by the orig_size variable.
+ The for loop stops before it gets to the signaled beams added above so that beams
+ added during this timestep are never dependent on each other for positioning.
+ */