code: def step(self, a):
      pos_before = mass_center(self.model, self.sim)
      self.do_simulation(a, self.frame_skip)
      pos_after = mass_center(self.model, self.sim)
  
      alive_bonus = 5.0
      data = self.sim.data
      lin_vel_cost = 1.25 * (pos_after - pos_before) / self.dt
      quad_ctrl_cost = 0.1 * np.square(data.ctrl).sum()
      quad_impact_cost = 0.5e-6 * np.square(data.cfrc_ext).sum()
      quad_impact_cost = min(quad_impact_cost, 10)
      reward = (
          lin_vel_cost - quad_ctrl_cost - quad_impact_cost + alive_bonus
      )
      qpos = self.sim.data.qpos
      terminated = bool((qpos[2] < 1.0) or (qpos[2] > 2.0))
  
      if self.render_mode == "human":
          self.render()
      return (
          self._get_obs(),
          reward,
          terminated,
          False,
          dict(
              reward_linvel=lin_vel_cost,
              reward_quadctrl=-quad_ctrl_cost,
              reward_alive=alive_bonus,
              reward_impact=-quad_impact_cost,
          ),
      )
  
file_path: gym/gym/envs/mujoco/humanoid.py
imports: import numpy
  from gym import utils
  from gym.envs.mujoco import MuJocoPyEnv
  from gym.spaces import Box
label_desc: Use image node_id 3 for calling the HumanoidEnv obj's underlying member method code with example usage: obj.step(a) and returns: self,  reward,  terminated,  False,  dict