https://pytorch.org/docs/stable/generated/torch.as_tensor.html
输入是ndarray时，如果device是cpu，对创建的tensor做修改，也会改变原ndarray的数值。
>>> a = numpy.array([1, 2, 3])
>>> t = torch.as_tensor(a)
>>> t
tensor([ 1, 2, 3])
>>> t[0] = -1
>>> a
array([-1, 2, 3])
>>> a = numpy.array([1, 2, 3])
>>> t = torch.as_tensor(a, device=torch.device('cuda'))
>>> t
tensor([ 1, 2, 3])
>>> t[0] = -1
>>> a
array([1, 2, 3])
