the output tensor having 1 fewer dimension than "input".
Parameters:
      * input (Tensor) -- the input tensor.
  * **dim** (*int*) -- the dimension to reduce.

  * **keepdim** (*bool*) -- whether the output tensor has "dim"
    retained or not.

Keyword Arguments:
      out (Tensor, optional) -- the output tensor.
Example:
  >>> a = torch.rand(4, 2).bool()
  >>> a
  tensor([[True, True],
          [True, False],
          [True, True],
          [True, True]], dtype=torch.bool)
  >>> torch.all(a, dim=1)
  tensor([ True, False,  True,  True], dtype=torch.bool)
  >>> torch.all(a, dim=0)
  tensor([ True, False], dtype=torch.bool)
