Example:
  >>> x = torch.zeros(5, 3)
  >>> t = torch.tensor([[1, 2, 3], [4, 5, 6], [7, 8, 9]], dtype=torch.float)
  >>> index = torch.tensor([0, 4, 2])
  >>> x.index_copy_(0, index, t)
  tensor([[ 1.,  2.,  3.],
          [ 0.,  0.,  0.],
          [ 7.,  8.,  9.],
          [ 0.,  0.,  0.],
          [ 4.,  5.,  6.]])
