code: def create_window(self, window_size, channel):
      _1D_window = self.gaussian(window_size, 1.5).unsqueeze(1)
      _2D_window = (
          _1D_window.mm(_1D_window.t()).unsqueeze(0).unsqueeze(0)
      )
      window = _2D_window.expand([channel, 1, window_size, window_size])
      return window
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import math
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle import ParamAttr
  from ppdet.core.workspace import register
  from ppdet.modeling import ops
  from ppdet.modeling.losses.iou_loss import GIoULoss
  from ppdet.utils.logger import setup_logger
label_desc: Use image node_id 3 for calling the SSIM obj's underlying member method code with example usage: obj.create_window(window_size, channel) and returns: window