element 0 of tensors does not require grad and does not have a grad_fn

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element 0 of tensors does not require grad and does not have a grad_fn

这个是因为requires_grad=False，应该为true

import numpy as np

import torch
from torch.autograd import Variable


x = Variable(torch.ones(2,2),requires_grad=False)
y = x + 2
# print(x.creator)      # None,用户直接创建没有creater属性
# print(y.creator)      # <torch.autograd._functions.basic_ops.AddConstant object at 0x7fb9b4d4b208>

z = y*y*3
out = z.mean()

out.backward()

print(x,y,z)
print(x.grad)          # 输出对out对x求倒结果
print(y.grad)          # y不是自动求导变量