Add new Losses to VISSL

VISSL allows adding new losses easily. Follow the steps below to add a new loss:

• Step1: Create a new loss my_new_loss in vissl/losses/my_new_loss.py following the template

import pprint
from classy_vision.losses import ClassyLoss, register_loss

@register_loss("my_new_loss")
class MyNewLoss(ClassyLoss):
    """
    Add documentation for what the loss does

    Config params:
        document what parameters should be expected for the loss in the defaults.yaml
        and how to set those params
    """

    def __init__(self, loss_config: AttrDict, device: str = "gpu"):
        super(MyNewLoss, self).__init__()

        self.loss_config = loss_config
        # implement what the init function should do
        ...

    @classmethod
    def from_config(cls, loss_config: AttrDict):
        """
        Instantiates MyNewLoss from configuration.

        Args:
            loss_config: configuration for the loss

        Returns:
            MyNewLoss instance.
        """
        return cls(loss_config)

    def __repr__(self):
        # implement what information about loss params should be
        # printed by print(loss). This is helpful for debugging
        repr_dict = {"name": self._get_name(), ....}
        return pprint.pformat(repr_dict, indent=2)

    def forward(self, output, target):
        # implement how the loss should be calculated. The output should be
        # torch.Tensor or List[torch.Tensor] and target should be torch.Tensor
        ...
        ...

        return loss

• Step2: Register the loss and loss params with VISSL Configuration. Add the params that the loss takes in VISSL defaults.yaml as follows:

LOSS:
  my_new_loss:
    param1: value1
    param2: value2
    ...

• Step3: Loss is ready to use. Simply set the configuration param LOSS.name=my_new_loss