code: def reduce_func(self, nodes):
      h_cat = nodes.mailbox["h"].view(nodes.mailbox["h"].size(0), -1)
      f = th.sigmoid(self.U_f(h_cat)).view(*nodes.mailbox["h"].size())
      c = th.sum(f * nodes.mailbox["c"], 1)
      return {"iou": self.U_iou(h_cat), "c": c}
  
imports: import itertools
  import time
  import dgl
  import networkx
  import numpy
  import torch
  import torch.nn
  import torch.nn.functional
label_desc: Use image node_id 3 for calling the TreeLSTMCell obj's underlying member method code with example usage: obj.reduce_func(nodes) and returns: dict