code: func NewUndirectedGraph(self, absent float64) *UndirectedGraph {
  	return &UndirectedGraph{
  		nodes: make(map[int]graph.Node),
  		edges: make(map[int]edgeHolder),
  
  		self:   self,
  		absent: absent,
  	}
  }
docs: // NewUndirectedGraph returns an UndirectedGraph with the specified self and absent
  // edge weight values.