Re: BGL and reversing / moving edges

From: joshrose (joshrose_at_[hidden])
Date: 2002-07-26 09:37:38

Thanks for the suggestion to use edge indices rather than descriptors
-- I'll give that a shot.  And thanks for helping me out!

-Josh
--- In Boost-Users_at_y..., Jeremy Siek <jsiek_at_c...> wrote:
> Hi Josh,
> 
> On Thu, 25 Jul 2002, joshrose wrote:
> joshro>
> joshro> However, I'm not sure this is quite what I'm looking for,
since in
> joshro> addition to not invalidating other iterators / descriptors
(those
> joshro> other than the one I'm trying to reverse), it's critical that I
> joshro> not invalidate the edge descriptor for the edge I'm trying to
> joshro> reverse, since it's still going to be in the graph, and property
> joshro> maps will refer to it.  What I think I really need is a way to
> joshro> move the edge within the graph (or at least remove the edge and
> joshro> re-add it, in a way that guarantees that the re-added edge
has the
> joshro> same edge_descriptor as the original edge).
> 
> Are you using internal property maps for the edges? Is so you, when you
> removed, and then add an edge, you could first read out all the property
> info, and then write it into the new edge.
> 
> If you are using an external map for edges... how are you doing the
> lookup? You aren't using the edge_descriptor itself as the key are you?
> That is bad... instead you could add an integer ID internal property for
> edges, and then use that to do lookups.
> 
> joshro> Tracing through the implementation a bit of add_edge, I have an
> joshro> idea on how to do this, but it involves a fair bit of
hacking and
> joshro> is not terribly clean (and probably doesn't work!):  you could
> joshro> directly go into the edge_desc_impl class (really it's
superclass
> joshro> edge_base) [from detail/edge.hpp] and swap the m_source and
> joshro> m_target members directly, then remove the edge from the source
> joshro> vertex edge list, create a StoredEdge instance and insert it
into
> joshro> the target edge list.  But I'm not sure how to link this new
> joshro> stored edge with the old edge_descriptor.
> 
> I suppose I could add the following function:
> 
> reverse_edge(edge_descriptor e, graph& g)
> 
> which would do what you are describing. However, if the property copying
> solution described above works for you, I'd rather not add the
> reverse_edge function.
> 
> Cheers,
> Jeremy
> 
> ----------------------------------------------------------------------
>  Jeremy Siek                          http://php.indiana.edu/~jsiek/
>  Ph.D. Student, Indiana Univ. B'ton   email: jsiek_at_o...
>  C++ Booster (http://www.boost.org)   office phone: [phone]
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