class_docstr: A fixed layer for calculating integral result from distribution.
  This layer calculates the target location by :math: `sum{P(y_i) * y_i}`,
  P(y_i) denotes the softmax vector that represents the discrete distribution
  y_i denotes the discrete set, usually {0, 1, 2, ..., reg_max}
  Args:
      reg_max (int): The maximal value of the discrete set. Default: 16. You
          may want to reset it according to your new dataset or related
          settings.
docstr: Forward feature from the regression head to get integral result of
  bounding box location.
  Args:
      x (Tensor): Features of the regression head, shape (N, 4*(n+1)),
          n is self.reg_max.
  Returns:
      x (Tensor): Integral result of box locations, i.e., distance
          offsets from the box center in four directions, shape (N, 4).
code: def forward(self, x):
      """Forward feature from the regression head to get integral result of
      bounding box location.
      Args:
          x (Tensor): Features of the regression head, shape (N, 4*(n+1)),
              n is self.reg_max.
      Returns:
          x (Tensor): Integral result of box locations, i.e., distance
              offsets from the box center in four directions, shape (N, 4).
      """
      x = F.softmax(x.reshape([-1, self.reg_max + 1]), axis=1)
      x = F.linear(x, self.project)
      if self.training:
          x = x.reshape([-1, 4])
      return x
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import math
  import numpy
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle import ParamAttr
  from paddle.nn.initializer import Normal, Constant
  from ppdet.core.workspace import register
  from ppdet.modeling.bbox_utils import distance2bbox, bbox2distance, batch_distance2bbox
  from ppdet.data.transform.atss_assigner import bbox_overlaps
label_desc: Use image node_id 2 for calling the Integral obj's underlying member method code with example usage: obj.forward(x) and returns: x