[Boost-users] Adding Vertex to Graph

I attempted to post this before but are not sure it went up so here it is again. Basically i have created a map with the key being a unique number and the value being a pointer to a class. Up until this point i have been using add_edge(1,2,graph) where 1 and 2 are unique numbers assigned to the classes. I now need to be able to add vertex and thought it would be something like add_vertex(3, graph) however it is not. How do i go about add a vertex with the id 3 Cheers Damian