Questions about GIoU computed in loss function.

[LMD0311]

Thanks for the inspiring work!

But I am confused by the use of not differentiable IoU in the loss function and differentiable GIoU in the matching cost. Or I misunderstanding the methods?

Another question is if there are $C$ classes, $N$ predictions and $M$ GTs, the shape of GIoU during matching will $(N,M)$, but the shape of $p_i$ is $(N,C)$, how to get $p_{i}f_{2}(s)$ ?