ones that are vectorized) may result in incorrect behavior. If
     you need to write to the tensors, please clone them first.
Example:
  >>> x = torch.tensor([[1], [2], [3]])
  >>> x.size()
  torch.Size([3, 1])
  >>> x.expand(3, 4)
  tensor([[ 1,  1,  1,  1],
          [ 2,  2,  2,  2],
          [ 3,  3,  3,  3]])
  >>> x.expand(-1, 4)   # -1 means not changing the size of that dimension
  tensor([[ 1,  1,  1,  1],
          [ 2,  2,  2,  2],
          [ 3,  3,  3,  3]])
