code: def vgg_ssd_loss(self):
      loss = fluid.layers.ssd_loss(
          self.face_mbox_loc,
          self.face_mbox_conf,
          self.face_box,
          self.gt_label,
          self.prior_boxes,
          self.box_vars,
          overlap_threshold=0.35,
          neg_overlap=0.35,
      )
      loss = fluid.layers.reduce_sum(loss)
      return loss
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import six
  import paddle.fluid
  from paddle.fluid.param_attr import ParamAttr
  from paddle.fluid.initializer import Xavier
  from paddle.fluid.initializer import Constant
  from paddle.fluid.initializer import Bilinear
  from paddle.fluid.regularizer import L2Decay
label_desc: Use image node_id 10 for calling the PyramidBox obj's underlying member method code with example usage: obj.vgg_ssd_loss() and returns: loss