of "diagonals"
Specifying a positive offset:
  >>> diags = torch.tensor([[1, 2, 3], [1, 2, 3], [1, 2, 3]])
  >>> torch.sparse.spdiags(diags, torch.tensor([0, 1, 2]), (5, 5)).to_dense()
  tensor([[1, 2, 3, 0, 0],
          [0, 2, 3, 0, 0],
          [0, 0, 3, 0, 0],
          [0, 0, 0, 0, 0],
          [0, 0, 0, 0, 0]])
