code: def forward(self, x):
      # down fpn
      f_down = self.FPN_Down_Fusion(x)
  
      # up fpn
      f_up = self.FPN_Up_Fusion(x)
  
      # fusion
      f_common = paddle.add(x=f_down, y=f_up)
      f_common = F.relu(f_common)
  
      if self.with_cab:
          # print('enhence f_common with CAB.')
          f_common = self.cross_attention(f_common)
  
      return f_common
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import paddle
  from paddle import nn
  import paddle.nn.functional
  from paddle import ParamAttr
label_desc: Use image node_id 2 for calling the SASTFPN obj's underlying member method code with example usage: obj.forward(x) and returns: f_common