code: def save_rpm(self):
      save_path = os.path.join(logger.get_dir(), "rpm.npz")
      self.rpm.save(save_path)
  
imports: import grpc
  import json
  import numpy
  import os
  import queue
  import simulator_pb2
  import simulator_pb2_grpc
  import six
  import time
  import threading
  from args import get_server_args
  from collections import defaultdict
  from concurrent import futures
  from multi_head_ddpg import MultiHeadDDPG
  from opensim_agent import OpenSimAgent
  from opensim_model import OpenSimModel
  from parl.utils import logger
  from replay_memory import ReplayMemory
  from utils import calc_indicators, ScalarsManager, TransitionExperience
label_desc: Use image node_id 9 for calling the SimulatorServer obj's underlying member method code with example usage: obj.save_rpm() without return types