code: def create_sync_ops(self, host_device):
      
      host_device = unify_device_name(host_device)
      sync_ops = []
      for layer in self.layers:
        if isinstance(layer, LayernGPU):
          sync_ops += layer.create_sync_ops(host_device)
      return sync_ops
docs: Return a list of assignment operations that syncs the parameters
      of all model copies with the one on host_device.
      :param host_device: (required str) the name of the device with latest
                          parameters