Note that the embedding vector at "padding_idx" is excluded
        from the reduction.
Return type:
      Tensor
Shape:
      * "input" (LongTensor) and "offsets" (LongTensor, optional)
    * If "input" is 2D of shape *(B, N)*, it will be treated as
      "B" bags (sequences) each of fixed length "N", and this will
      return "B" values aggregated in a way depending on the
      "mode". "offsets" is ignored and required to be "None" in
      this case.

    * If "input" is 1D of shape *(N)*, it will be treated as a
      concatenation of multiple bags (sequences). "offsets" is
      required to be a 1D tensor containing the starting index
      positions of each bag in "input". Therefore, for "offsets"
      of shape *(B)*, "input" will be viewed as having "B" bags.
      Empty bags (i.e., having 0-length) will have returned
      vectors filled by zeros.

  * "weight" (Tensor): the learnable weights of the module of
