target_pos = target.bool()
target_neg = ~target_pos
# loss_pos and loss_neg below contain non-zero values only for those elements
# that are positive pairs and negative pairs respectively.
loss_pos = torch.zeros(x.size(0), x.size(0)).masked_scatter(target_pos, loss[target_pos])
loss_neg = torch.zeros(x.size(0), x.size(0)).masked_scatter(target_neg, loss[target_neg])