def prepare_target(self, y):
        """
        Prepare target before training.

        Parameters
        ----------
        y : a :tensor: `torch.Tensor`
            Target matrix.

        Returns
        -------
        `torch.Tensor`
            Converted target matrix.
        """
        raise NotImplementedError(
            "users must define prepare_target to use this base class"
        )

        Prepare target before training.

        Parameters
        ----------
        y : a :tensor: `torch.Tensor`
            Target matrix.

        Returns
        -------
        `torch.Tensor`
            Converted target matrix.
        
pytorch_tabnet/abstract_model.py