def reduce(
        self,
        tensor: Union[Tensor, Any],
        group: Optional[Any] = None,
        reduce_op: Optional[Union[ReduceOp, str]] = "mean",
    ) -> Union[Tensor, Any]:
        """Reduces the given tensor (e.g. across GPUs/processes).

        Args:
            tensor: the tensor to sync and reduce
            group: the process group to reduce
            reduce_op: the reduction operation. Defaults to 'mean'.
                Can also be a string 'sum' or ReduceOp.

        """
Reduces the given tensor (e.g. across GPUs/processes).

        Args:
            tensor: the tensor to sync and reduce
            group: the process group to reduce
            reduce_op: the reduction operation. Defaults to 'mean'.
                Can also be a string 'sum' or ReduceOp.

        
src/lightning/pytorch/strategies/strategy.py