code: def forward(self, x, pos):
      dists = square_distance(pos, pos)
      knn_idx = dists.argsort()[:, :, : self.n_neighbors]  # b x n x k
      knn_pos = index_points(pos, knn_idx)
  
      h = self.fc1(x)
      q, k, v = (
          self.w_qs(h),
          index_points(self.w_ks(h), knn_idx),
          index_points(self.w_vs(h), knn_idx),
      )
  
      pos_enc = self.fc_delta(
          pos[:, :, None] - knn_pos
      )  # b x n x k x f
  
      attn = self.fc_gamma(q[:, :, None] - k + pos_enc)
      attn = torch.softmax(
          attn / np.sqrt(k.size(-1)), dim=-2
      )  # b x n x k x f
  
      res = torch.einsum("bmnf,bmnf->bmf", attn, v + pos_enc)
      res = self.fc2(res) + x
      return res, attn
  
imports: import numpy
  import torch
  from helper import index_points, square_distance, TransitionDown, TransitionUp
  from torch import nn
label_desc: Use image node_id 2 for calling the PointTransformerBlock obj's underlying member method code with example usage: obj.forward(x, pos) and returns: res,  attn