deprecated, and in the meantime, specifying either of those
        two args will override "reduction". Default: "'mean'"
Shape:
      * Input1: (N, D) or (D), where N is the batch size and D is
        the embedding dimension.
  * Input2: (N, D) or (D), same shape as Input1.

  * Target: (N) or ().

  * Output: If "reduction" is "'none'", then (N), otherwise
    scalar.
