


torch.cov(x, correction=0)
      tensor([[ 0.6667, -0.6667],
              [-0.6667,  0.6667]])
      >>> fw = torch.randint(1, 10, (3,))
      >>> fw
      tensor([1, 6, 9])
      >>> aw = torch.rand(3)
      >>> aw
      tensor([0.4282, 0.0255, 0.4144])
      >>> torch.cov(x, fweights=fw, aweights=aw)
      tensor([[ 0.4169, -0.4169],
              [-0.4169,  0.4169]])


