class_docstr: DQN that allows maxQ also backpropagate gradients.
code: def sync_target_network(self):
      pass
  
file_path: chainerrl/chainerrl/agents/residual_dqn.py
imports: from chainerrl.agents.dqn import DQN
  from chainerrl.functions import scale_grad
label_desc: Use image node_id 2 for calling the ResidualDQN obj's underlying member method code with example usage: obj.sync_target_network() without return types