Subject: Re: [Boost-users] [BGL] A* queue size not mutable
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2009-12-26 15:34:25
On Tue, 22 Dec 2009, Arnaud Masserann wrote:
> Where are you looking? The line I see (in astar_search_no_init) is:
>
> MutableQueue Q(cost, index_in_heap, compare);
>
> which doesn't require the number of vertices in advance.
>
>
> So implicit graphs have been implemented since boost 1.39 ... Are you aware of any implementation notes, documentation, reference ? I'll give it a try tonight.
>
I don't think there is separate documentation; allowing implicit graphs
was a fix for a bug that was in Trac.
> Notes :
> I use astar_search_no_init, and property maps based on std::map so that put() can index it in a not-known-yet location.
> Btw, my color map type is std::map<NodeID,boost::default_color_type > (plus the wrapper around it). I feel that using
> "boost::default_color_type" is kind of a hack. Is it ?
>
>
> The reason is that the normal Boost A* search avoids processing the same vertex twice by using a color map. If you want the implicit graph version that
> appears in most textbooks, you need a dummy color map that claims that all vertices are unvisited. So it is somewhat a workaround to allow the same
> algorithm to work for both cases.
>
>
> That was not exactly my question. The thing is, I discovered the type "boost::default_color_type" while watching internal boost headers I'm not really supposed
> to look at as an end-user. I feel like I should have used something like boost::color_map::type or whatever. This would be exactly the same from the compiler's
> point of view, but the code would be better.
> More importantly, what are the logical steps I should have done to figure it out ?
>
You could define your own color type if you want as well. It would
probably be difficult to figure out, though. It might be better to have a
tree search version of A* that automatically does _no_init and a fake
color map. Could you please submit a feature request on svn.boost.org for
this functionality? Thank you.
-- Jeremiah Willcock