text: import torch
  
  x = torch.ones(2,2,requires_grad=True) # 生成2*2的矩阵  默认初始值为1
  print(x)
  
  y = x + 2
  z = y *y + 3
  out = z.mean()
  print(y)
  print(z)
  print(out)
  
  # 计算梯度
  out.backward()
  
  print(x.grad)
  
  with torch.no_grad():  # 忽略梯度
      k = x + 1
      print(k)
      
      
  k = x + 1
  print(k)