---------------------------------------------------------------------------
RuntimeError Traceback (most recent call last)
<ipython-input-178-212068df461b> in <module>
15 done = env_info.local_done[0] # see if episode has finished
16 transition = (state, action, reward, next_state, done) #set transition
---> 17 agent.step(transition) # step into the next state
18 score += reward # update the score
19 state = next_state # roll over the state to next time step
<ipython-input-173-50233688ff15> in step(self, transition)
42 if(len(self.memory) > BATCH_SIZE):
43 experiences = self.memory.sample()
---> 44 self.train(experiences)
45
46 def get_action(self, state, eps=0.0):
<ipython-input-173-50233688ff15> in train(self, experiences)
84 loss = F.mse_loss(Q_expected, Q_targets)
85 self.optimizer.zero_grad()
---> 86 loss.backward()
87 self.optimizer.step()
88
~/opt/anaconda3/envs/drlnd/lib/python3.6/site-packages/torch/tensor.py in backward(self, gradient, retain_graph, create_graph)
196 products. Defaults to ``False``.
197 """
--> 198 torch.autograd.backward(self, gradient, retain_graph, create_graph)
199
200 def register_hook(self, hook):
~/opt/anaconda3/envs/drlnd/lib/python3.6/site-packages/torch/autograd/__init__.py in backward(tensors, grad_tensors, retain_graph, create_graph, grad_variables)
98 Variable._execution_engine.run_backward(
99 tensors, grad_tensors, retain_graph, create_graph,
--> 100 allow_unreachable=True) # allow_unreachable flag
101
102
RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn```