Multi-Label Soft Margin loss (#27669)
Summary:
In accordance with https://github.com/pytorch/pytorch/issues/25883, I added the `MultiLabelSoftMarginLoss` module and `multilabel_soft_margin_loss` functional.
It looks like there isn't a C++ ATen implementation of `multilabel_soft_margin_loss`, so I translated the python version, which does not rely on a C/C++ backend either.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27669
Differential Revision: D17907608
Pulled By: yf225
fbshipit-source-id: ccb02951e009973c2adbe604593ce929f10c39eb
