


torch.sum(a, 1)
      tensor([-0.4598, -0.1381,  1.3708, -2.6217])
      >>> b = torch.arange(4 * 5 * 6).view(4, 5, 6)
      >>> torch.sum(b, (2, 1))
      tensor([  435.,  1335.,  2235.,  3135.])


