docstr: update actor and critic model with MADDPG algorithm
          
docstr_tok: ["update","actor","and","critic","model","with","MADDPG","algorithm"]
code: def learn(self, obs_n, act_n, target_q):
      """update actor and critic model with MADDPG algorithm"""
      actor_cost = self._actor_learn(obs_n, act_n)
      critic_cost = self._critic_learn(obs_n, act_n, target_q)
      self.sync_target()
      return critic_cost
  
file_path: PARL/parl/algorithms/paddle/maddpg.py
imports: import parl
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from parl.utils.utils import check_model_method
  from copy import deepcopy
label_desc: Use image node_id 5 for calling the MADDPG obj's underlying member method code with example usage: obj.learn(obs_n, act_n, target_q) and returns: critic_cost