code: def forward(self):
      relative_position_bias = self.relative_position_bias_table[
          self.relative_position_index.reshape([-1])
      ].reshape(
          [
              self.window_size[0] * self.window_size[1] + 1,
              self.window_size[0] * self.window_size[1] + 1,
              -1,
          ]
      )  # Wh*Ww,Wh*Ww,nH
      return relative_position_bias.transpose((2, 0, 1))
  
imports: import math
  import paddle
  import paddle.nn
  import paddle.nn.functional
  import numpy
  from paddle.nn.initializer import Constant
  from ppdet.modeling.shape_spec import ShapeSpec
  from ppdet.core.workspace import register, serializable
  from .transformer_utils import zeros_, DropPath, Identity
label_desc: Use image node_id 2 for calling the RelativePositionBias obj's underlying member method code with example usage: obj.forward() and returns: relative_position_bias