Why Constraiting IoU target to [-1, 1]?

[ihaohe]

Thanks for you great work. I've some question about the IoU target. Why do you constrait the IoU target to [-1, 1] by using iout = 2 · (iou − 0.5) ? Does it regress more easily?

[hejiakia]

Maybe the output of iou is between [0, 1]