code: def __call__(self, preds, targets):
      heatmap, mask = targets
      loss = (preds - heatmap) ** 2 * mask.cast("float").unsqueeze(1)
      loss = paddle.clip(loss, min=0, max=2).mean()
      loss *= self.loss_factor
      return loss
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from itertools import cycle, islice
  from collections import abc
  import numpy
  import paddle
  import paddle.nn
  from ppdet.core.workspace import register, serializable
label_desc: Use image node_id 2 for calling the HeatMapLoss obj's underlying member method code with example usage: obj.__call__(preds, targets) and returns: loss