to be a Tensor of size nbatch.
  * **size_average** (*bool**, **optional*) -- Deprecated (see
    "reduction"). By default, the losses are averaged over each
    loss element in the batch. Note that for some losses, there
    are multiple elements per sample. If the field "size_average"
    is set to "False", the losses are instead summed for each
    minibatch. Ignored when "reduce" is "False". Default: "True"

  * **reduce** (*bool**, **optional*) -- Deprecated (see
    "reduction"). By default, the losses are averaged or summed
    over observations for each minibatch depending on
    "size_average". When "reduce" is "False", returns a loss per
    batch element instead and ignores "size_average". Default:
    "True"

  * **reduction** (*str**, **optional*) -- Specifies the reduction
    to apply to the output: "'none'" | "'mean'" | "'sum'".
    "'none'": no reduction will be applied, "'mean'": the sum of
