Initial state of vector (or array?), I do not understand

The 2 lines refer to x_2

You show them with point in draw().

But I think the } } are a bit wrong and somehow the point command is outside the for loop.

You can always use ctrl-t in processing prior to posting to get auto-indents.

Setup() is run only once. Your box values are very high so the x,y points will be outside of the canvas?