[xb](https://docs.pytorch.org/docs/stable/tensors.html#torch.Tensor "torch.Tensor") = [x_train](https://docs.pytorch.org/docs/stable/tensors.html#torch.Tensor "torch.Tensor")[start_i:end_i]
[yb](https://docs.pytorch.org/docs/stable/tensors.html#torch.Tensor "torch.Tensor") = [y_train](https://docs.pytorch.org/docs/stable/tensors.html#torch.Tensor "torch.Tensor")[start_i:end_i]