code: def calc_vel_diff(state_desc):
      cur_vel_x = state_desc["body_vel"]["pelvis"][0]
      cur_vel_z = state_desc["body_vel"]["pelvis"][2]
      target_vel_x = state_desc["target_vel"][0]
      target_vel_z = state_desc["target_vel"][2]
      diff_vel_x = cur_vel_x - target_vel_x
      diff_vel_z = cur_vel_z - target_vel_z
  
      cur_vel = (cur_vel_x**2 + cur_vel_z**2) ** 0.5
      target_vel = (target_vel_x**2 + target_vel_z**2) ** 0.5
      diff_vel = cur_vel - target_vel
  
      target_theta = math.atan(-1.0 * target_vel_z / target_vel_x)
      # alone y axis
      cur_theta = state_desc["body_pos_rot"]["pelvis"][1]
      diff_theta = cur_theta - target_theta
  
      return (
          cur_vel_x,
          cur_vel_z,
          diff_vel_x,
          diff_vel_z,
          diff_vel,
          diff_theta,
      )
  
imports: import abc
  import copy
  import gym
  import math
  import numpy
  from collections import OrderedDict
  from osim.env import ProstheticsEnv
  from parl.utils import logger
label_desc: Use image node_id 1 for calling a global function with example usage: calc_vel_diff(state_desc) and returns: cur_vel_x,  cur_vel_z,  diff_vel_x,  diff_vel_z,  diff_vel,  diff_theta