docstr: Learn the value model with square error cost
          
docstr_tok: ["Learn","the","value","model","with","square","error","cost"]
code: def value_learn(self, obs, val):
      """Learn the value model with square error cost"""
      predict_val = self.model.value(obs)
      loss = layers.square_error_cost(predict_val, val)
      loss = layers.reduce_mean(loss)
      optimizer = fluid.optimizer.AdamOptimizer(self.value_lr)
      optimizer.minimize(loss)
      return loss
  
file_path: PARL/parl/algorithms/fluid/ppo.py
imports: import warnings
  import numpy
  from copy import deepcopy
  from paddle import fluid
  from parl.core.fluid import layers
  from parl.core.fluid.algorithm import Algorithm
label_desc: Use image node_id 8 for calling the PPO obj's underlying member method code with example usage: obj.value_learn(obs, val) and returns: loss