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'"
Shape:
      * Input: (*) where * means, any number of dimensions. The sum
        operation operates over all the elements.
  * Target: (*), same shape as the input

  * Output: scalar. If "reduction" is "'none'", then same shape as
    the input
