3.6.7章节运行train_ch3函数报错

[cdrj]

bug描述
num_epochs, lr = 5, 0.1
d2l.train_ch3(net, train_iter, test_iter, cross_entropy, num_epochs, batch_size, [W, b], lr)

---

RuntimeError Traceback (most recent call last)
in
2
3
----> 4 d2l.train_ch3(net, train_iter, test_iter, cross_entropy, num_epochs, batch_size, [W, b], lr)

~\动手深度学习\d2lzh_pytorch\utils.py in train_ch3(net, train_iter, test_iter, loss, num_epochs, batch_size, params, lr, optimizer)
132 param.grad.data.zero_()
133
--> 134 l.backward()
135 if optimizer is None:
136 sgd(params, lr, batch_size)

C:\ProgramData\Anaconda3\envs\pytorch\lib\site-packages\torch\tensor.py in backward(self, gradient, retain_graph, create_graph)
193 products. Defaults to False.
194 """
--> 195 torch.autograd.backward(self, gradient, retain_graph, create_graph)
196
197 def register_hook(self, hook):

C:\ProgramData\Anaconda3\envs\pytorch\lib\site-packages\torch\autograd_init_.py in backward(tensors, grad_tensors, retain_graph, create_graph, grad_variables)
97 Variable._execution_engine.run_backward(
98 tensors, grad_tensors, retain_graph, create_graph,
---> 99 allow_unreachable=True) # allow_unreachable flag
100
101

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

版本信息
pytorch:
torchvision:1.4.0
torchtext:
...