code: def forward(self, v, batch):
      v = self.lin1(v)
      v = self.act(v)
      v = self.lin2(v)
      u = scatter(v, batch, dim=0)
      return u
  
imports: from math import pi
  import torch
  import torch.nn.functional
  from torch.nn import Embedding, Sequential, Linear
  from torch_scatter import scatter
  from torch_geometric.nn import radius_graph
label_desc: Use image node_id 3 for calling the update_u obj's underlying member method code with example usage: obj.forward(v, batch) and returns: u