code: def forward(self, nodes):
      msg_input = nodes.data["msg_input"]
      msg_delta = self.W_h(nodes.data["accum_msg"])
      msg = F.relu(msg_input + msg_delta)
      return {"msg": msg}
  
imports: import dgl
  import dgl.function
  import rdkit.Chem
  import torch
  import torch.nn
  import torch.nn.functional
  from dgl import line_graph, mean_nodes
  from .chemutils import get_mol
label_desc: Use image node_id 2 for calling the LoopyBPUpdate obj's underlying member method code with example usage: obj.forward(nodes) and returns: dict