def inverse(self):
        """
        Return the inverse of the graph.
        
        @rtype:  graph
        @return: Complement graph for the graph.
        """
        inv = self.__class__()
        inv.add_nodes(self.nodes())
        inv.complete()
        for each in self.edges():
            if (inv.has_edge(each)):
                inv.del_edge(each)
        return inv
Return the inverse of the graph.
        
        @rtype:  graph
        @return: Complement graph for the graph.