code: def _create_complete_graph(node_ids):
      
      g = nx.Graph()
      g.add_nodes_from(node_ids)
      for (i, j) in combinations(node_ids, 2):
          g.add_edge(i, j)
      return g
docs: Create a complete graph from the list of node ids.
  
      Args:
          node_ids: a list of node ids
  
      Returns:
          An undirected graph (as a networkx.Graph)