torch.Tensor.to_dense
Tensor.to_dense() -> Tensor
Creates a strided copy of "self" if "self" is not a strided tensor,
   otherwise returns "self".
Example:
  >>> s = torch.sparse_coo_tensor(
  ...        torch.tensor([[1, 1],
  ...                      [0, 2]]),
  ...        torch.tensor([9, 10]),
  ...        size=(3, 3))
  >>> s.to_dense()
  tensor([[ 0,  0,  0],
          [ 9,  0, 10],
          [ 0,  0,  0]])
