code: def _df_loss(self, pred_dist, target, lower_bound=0):
      target_left = paddle.cast(target.floor(), "int64")
      target_right = target_left + 1
      weight_left = target_right.astype("float32") - target
      weight_right = 1 - weight_left
      loss_left = (
          F.cross_entropy(
              pred_dist, target_left - lower_bound, reduction="none"
          )
          * weight_left
      )
      loss_right = (
          F.cross_entropy(
              pred_dist, target_right - lower_bound, reduction="none"
          )
          * weight_right
      )
      return (loss_left + loss_right).mean(-1, keepdim=True)
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.core.workspace import register
  from paddle import ParamAttr
  from paddle.nn.initializer import KaimingNormal
  from paddle.nn.initializer import Normal, Constant
  from ..bbox_utils import batch_distance2bbox
  from ..losses import GIoULoss
  from ..initializer import bias_init_with_prob, constant_, normal_
  from ..assigners.utils import generate_anchors_for_grid_cell
  from ppdet.modeling.backbones.cspresnet import ConvBNLayer, RepVggBlock
  from ppdet.modeling.ops import get_static_shape, get_act_fn
  from ppdet.modeling.layers import MultiClassNMS
label_desc: Use image node_id 13 for calling the PPYOLOEHead obj's underlying member method code with example usage: obj._df_loss(pred_dist, target, lower_bound) and returns: unknown