code: function simpleSizeForMultiGraphs(graph) {
    var nodes = graph.nodes(),
        size = 0,
        i,
        l;
  
    for (i = 0, l = nodes.length; i < l; i++) {
      size += graph.outNeighbors(nodes[i]).length;
      size += graph.undirectedNeighbors(nodes[i]).length / 2;
    }
  
    return size;
  }
docs: Returns the size a multi graph would have if it were a simple one.
  
  @param  {Graph}  graph - Target graph.
  @return {number}