fixed reward callback

Author: ryan-lowe

multiagent/environment.py

@@ -129,7 +129,7 @@ def _get_obs(self, agent):
  def _get_reward(self, agent):
  if self.reward_callback is None:
  return 0.0
- self.reward_callback(agent, self.world)
+ return self.reward_callback(agent, self.world)
 
  # set env action for a particular agent
  def _set_action(self, action, agent, action_space, time=None):