"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.
  * Target: (*), same shape as the input.

Examples:
  >>> loss = nn.MSELoss()
  >>> input = torch.randn(3, 5, requires_grad=True)
  >>> target = torch.randn(3, 5)
  >>> output = loss(input, target)
  >>> output.backward()
