# Need help in understanding the question

I have a problem in understanding the sentence

Alpha indicates the IoU (Intersection over Union) for neighbouring candidate boxes; step sizes of the sliding windows are determined such that one step results in an IoU of Alpha.

What I understand is: The value of Alpha (which is step size) is actually the IoU (Intersection over Union) for neighbouring candidate boxes ;(further explanation of this previous sentence.) step sizes of the sliding windows can be calculated as one step produce in an IoU of Alpha.

I didn't understand the meaning of "in an IoU of Alpha."

• I think I get it. α=N÷U, and "sliding windows" (whatever they are) are selected such that the value of α for each is always the same. But without context, and maybe the diagram or three from the source of the original statement, it's really difficult to plug yourself into some random subject matter. Jan 8, 2017 at 9:37
• sorry, what is N÷U? Jan 8, 2017 at 9:42
• The number in the intersection divided by the number in the union. Set theory. If your statement has nothing to do with set theory, that shows just why it's necessary to give complete context. Jan 8, 2017 at 9:43
• In my area, IoU is defined as "dividing the area of overlap between the bounding boxes by the area of union" . So, 'in an IoU of Alpha' means values of Alpha is always same as IoU? Jan 8, 2017 at 9:48
• OK, so it's area of intersection rather than number. I was nearly right on that. Without complete context though, I'm not going to be able to get any further. If you think that what you have given is enough, then you might be able to get someone on Mathematics or Cross Validated to interpret it -- but it's not even clear what your "area" is and whether those sites will know instinctively what you're referring to. Jan 8, 2017 at 9:52