is "linear".
  * **out** (*Tensor**, **optional*) -- the output tensor.

Example:
  >>> t = torch.tensor([float('nan'), 1, 2])
  >>> t.quantile(0.5)
  tensor(nan)
  >>> t.nanquantile(0.5)
  tensor(1.5000)
  >>> t = torch.tensor([[float('nan'), float('nan')], [1, 2]])
  >>> t
  tensor([[nan, nan],
          [1., 2.]])
  >>> t.nanquantile(0.5, dim=0)
  tensor([1., 2.])
  >>> t.nanquantile(0.5, dim=1)
  tensor([   nan, 1.5000])
