有两种方式直接把模型的参数梯度设成0：
model.zero_grad() optimizer.zero_grad() # 当optimizer=optim.Optimizer(model.parameters())时，两者等效如果想要把某一Variable的梯度置为0，只需用以下语句：
Variable.grad.data.zero_()
# Zero the gradients before running the backward pass. model.zero_grad() # Before the backward pass, use the optimizer object to zero all of the # gradients for the variables it will update (which are the learnable weights # of the model) optimizer.zero_grad()
