code: def train():
      model.train()
      optimizer.zero_grad()
      F.nll_loss(
          model()[data.train_mask], data.y[data.train_mask]
      ).backward()
      optimizer.step()
  
file_path: pytorch_geometric/examples/sgc.py
imports: import os.path
  import torch
  import torch.nn.functional
  from torch_geometric.datasets import Planetoid
  from torch_geometric.nn import SGConv
label_desc: Use image node_id 1 for calling a global function with example usage: train() without return types