Re: BGL and reversing / moving edges

From: joshrose (joshrose_at_[hidden])
Date: 2002-07-25 12:06:21

Quick clarification -- I really didn't mean to say that I want
edge iterators to be stable -- that doesn't really make much
sense, since I'm changing the link structure of the graph.  Instead,
I'm really focusing on having a stable edge_descriptor, since that is
refered to by long-lived entities (e.g. property maps).

Thanks,

-Josh

--- In Boost-Users_at_y..., "joshrose" <joshrose_at_y...> wrote:
> This is an interesting idea -- I do have the requirement that
parallel
> edges are allowed (think of the point of the algorithm as reducing a
> muti-graph to a standard graph, s.t. the sum of all edge weights is
> maximal), so neither hash_setS nor setS would work.  But, multisets
> appear to be an option, using the mutisetS selector.  I think you're
> suggesting that I can use one of these other edgelist
> implementatations, then remove and re-add the edge.
> 
> However, I'm not sure this is quite what I'm looking for, since in
> addition to not invalidating other iterators / descriptors (those
> other than the one I'm trying to reverse), it's critical that I not
> invalidate the edge descriptor for the edge I'm trying to reverse,
> since it's still going to be in the graph, and property maps will
> refer to it.  What I think I really need is a way to move the edge
> within the graph (or at least remove the edge and re-add it, in a
way
> that guarantees that the re-added edge has the same edge_descriptor
as
> the original edge).
> 
> Tracing through the implementation a bit of add_edge, I have an idea
> on how to do this, but it involves a fair bit of hacking and is not
> terribly clean (and probably doesn't work!):  you could directly go
> into the edge_desc_impl class (really it's superclass edge_base)
[from
> detail/edge.hpp] and swap the m_source and m_target members
directly,
> then remove the edge from the source vertex edge list, create a
> StoredEdge instance and insert it into the target edge list.  But
I'm
> not sure how to link this new stored edge with the old
> edge_descriptor.
> 
> Does this help clear things up?
> 
> Again, thanks for the reply.
> 
> -Josh
> 
> --- In Boost-Users_at_y..., "Matthias Kronenberger" <mkronen_at_r...>
wrote:
> > You could use hash_setS or setS for the Edge_list.
> > This will allow you to remove edges and add edges without
> invalidating edge
> > iterators or edge descriptors.