code: def compare_costs(prev_cost, new_cost) -> float:
      """Compare the previous cost and the new cost.
  
      Args:
          prev_cost (float): the previous cost
          new_cost (float): the updated cost
  
      Returns:
          float: the ratio between these two costs
      """
      return (new_cost - prev_cost) / prev_cost
  
label_desc: Use image node_id 2 for calling a global function with example usage: compare_costs(prev_cost, new_cost) and returns: unknown