code: def r3d_18_flow(pretrained=False, progress=True, **kwargs):
      """Construct 18 layer Resnet3D model for optical flow."""
  
      return _video_resnet_flow(
          "r3d_18",
          pretrained,
          progress,
          block=BasicBlock,
          conv_makers=[Conv3DSimple] * 4,
          layers=[2, 2, 2, 2],
          stem=BasicFLowStem,
          **kwargs,
      )
  
imports: import torch.nn
  from torch.hub import load_state_dict_from_url
label_desc: Use image node_id 4 for calling a global function with example usage: r3d_18_flow(pretrained, progress) and returns: _video_resnet_flow