class_docstr: FCOSR Head, refer to https://arxiv.org/abs/2111.10780 for details 
class_docstr_tok: ["FCOSR","Head",",","refer","to","https",":","\/\/arxiv.org\/abs\/2111.10780","for","details"]
code: def _qfocal_loss(score, label, gamma=2.0, reduction="sum"):
      weight = (score - label).pow(gamma)
      loss = F.binary_cross_entropy(
          score, label, weight=weight, reduction=reduction
      )
      return loss
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.core.workspace import register
  from paddle import ParamAttr
  from paddle.regularizer import L2Decay
  from .fcos_head import ScaleReg
  from ..initializer import bias_init_with_prob, constant_, normal_
  from ..ops import get_act_fn, anchor_generator
  from ..rbox_utils import box2corners
  from ..losses import ProbIoULoss
  import numpy
label_desc: Use image node_id 11 for calling the FCOSRHead obj's underlying member method code with example usage: obj._qfocal_loss(score, label, gamma, reduction) and returns: loss