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)
      return critic_cost
  
file_path: PARL/parl/algorithms/fluid/maddpg.py
imports: import warnings
  from parl.core.fluid import layers
  from copy import deepcopy
  from paddle import fluid
  from parl.core.fluid.algorithm import Algorithm
  from parl.core.fluid.policy_distribution import SoftCategoricalDistribution
  from parl.core.fluid.policy_distribution import SoftMultiCategoricalDistribution
label_desc: Use image node_id 6 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