code: function findLCA(node1, node2, layoutInfo) {
    // Find their common ancester, starting from the root graph
    var res = findLCA_aux(node1, node2, 0, layoutInfo);
  
    if (2 > res.count) {
      // If aux function couldn't find the common ancester,
      // then it is the root graph
      return 0;
    } else {
      return res.graph;
    }
  }
docs: @brief : This function finds the index of the lowest common
  graph ancestor between 2 nodes in the subtree
  (from the graph hierarchy induced tree) whose
  root is graphIx
  
  @arg node1: node1's ID
  @arg node2: node2's ID
  @arg layoutInfo: layoutInfo object