to apply to the output: "'none'" | "'mean'" | "'sum'".
        "'none'": no reduction will be applied, "'mean'": the sum of
        the output will be divided by the number of elements in the
        output, "'sum'": the output will be summed. Note:
        "size_average" and "reduce" are in the process of being
        deprecated, and in the meantime, specifying either of those
        two args will override "reduction". Default: "'mean'"
Return type:
      Tensor