code: def freeze(self, model_ref: str):
      assert model_ref in self.submodules
      model = getattr(self, model_ref)
      model.eval()
      for param in model.parameters():
          param.stop_gradient = True
  
file_path: PaddleDetection/ppdet/modeling/architectures/multi_stream_detector.py
imports: from typing import Dict
  from collections import OrderedDict
  from ppdet.modeling.architectures.meta_arch import BaseArch
label_desc: Use image node_id 5 for calling the MultiSteamDetector obj's underlying member method code with example usage: obj.freeze(model_ref) without return types