Hello, authors! I have diffculty understanding this [line](https://github.com/fnzhan/MoNCE/blob/1a666e26f4312db6867db7ba754e4f6901c6fde5/CUT_MoNCE/models/sinkhorn.py#L33) of code. ``` C = torch.einsum('bid,bod->bio', q, k) ``` What does torch.einsum do here? Could you provide a simple example? Thanks!