作业1-2：模型最优参数选择

获取模型参数的梯度

def get_p_norm(model):
    grad_all = 0.0
    for p in model.parameters():
        grad = 0.0
        if p.grad is not None:
            # print("max grad is {} ".format(p.grad.max()))
            grad = (p.grad ** 2).sum()
        grad_all += grad
    grad_norm = grad_all ** 0.5
    return grad_norm