[Boost-users] Completely Perplexed Noob to BGL: Reachability Question

Subject: [Boost-users] Completely Perplexed Noob to BGL: Reachability Question
From: Roshan Rammohan (roshan.r_at_[hidden])
Date: 2009-03-26 06:08:11

Hi all,

 Although I was attracted to BGL since I have to use a lot of graph
algorithms for my work, and I have managed to read through as much online
documentation as possible,
 generic programming is still very mysterious to me.

 All I need to do is compute reachability from vertex B to vertex A before I
add the edge A->B to a graph (directed and acyclic) so that I can maintain
its acyclic property.
 I do not want to add the edge, discover a cycle and then remove it.

 I saw a very closely related example here. (thanks to Steven Watanabe)
 http://lists.boost.org/boost-users/2009/03/46396.php

 That was helpful, but I'm still not able to adapt this to my need mainly
because I find the syntax and concepts of generic programming extremely
confusing.

 I am not sure how I can pass an extra parameter into a BFSVisitor which the
member function discover_vertex can use. Does discover_vertex have to have
only a vertex_descriptor and a Graph?
 I want to pass another constant vertex to it so I can return on equality.

 I need to initiate a BFS from vertex B, (and not continue with new trees
once the tree with B as root is finished) .
 On discovering vertex A in this search I need to return true, false for all
other cases.

 Pretty simple, and I am hoping someone would write a code snippet for me
that will solve the problem and also provide me with the baby step I need
to  wrap my head around this Visitor concept.

 Thanks in advance.

 - Roshan Rammohan
 PhD Candidate, A.I. lab, Dept of C.S.,
 Univ. of New Mexico, USA