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Subject: Re: [Boost-users] Default weight map doesn't work for weighted grid graph in A-star search
From: W.P. McNeill (billmcn_at_[hidden])
Date: 2010-07-14 17:12:35

I seed the random number generator once at the top of main(). This is
sufficient to generate a different random maze every time the program is run
or if multiple random mazes were to be created in the same run.

On Wed, Jul 14, 2010 at 1:43 PM, Jeremiah Willcock <jewillco_at_[hidden]>wrote:

> On Wed, 14 Jul 2010, W.P. McNeill wrote:
> A-Star-Maze solver is pretty much done. The filtered_graph does make the
>> code a lot simpler. I used lexical_cast and Boost's random number
>> facilities, but decided the Boost command line processing code was overkill
>> for this example. The warnings you added about not subclassing BGL types
>> look good.
> OK.
> Two things that look like documentation errors:
>> 1. On the A* search page, the examine_vertex prototype for the visitor is
>> listed as vis.examine_vertex(u, g), but you actually need it to
>> be vis.examine_vertex(u, const g) in order for the code the build.
>> (This may be true for the other visitor functions as well.) This tripped
>> me up when
>> I first wrote my visitor class. I'm not sure if you want to specify
>> the constants here, or let them be assumed.
>> 2. The grid graph indexing documentation incorrectly states that you get
>> a vertex index with get(boost::vertex_index, vertex_descriptor, const
>> Graph&).
>> The order of the last two parameters is switched. The header actually
>> specifies get(boost::vertex_index, const Graph&, vertex_descriptor). This
>> appears to be the case in the documentation for a number of the
>> get(...) functions.
> I believe I fixed both of these now. Please check.
> BTW, you don't need to create your own weight map if the weights are all
> the same; just use something like static_property_map<double>(1.) as the
> weight map. Also, why do you need your own vertex index map? It appears to
> just forward to the grid graph's version; why not just use that one
> directly? It appears that filtered_graph forwards property map requests to
> the underlying graph by default anyway, so you might just be able to remove
> that argument from your call to astar_search. You also don't need to call
> num_vertices() on the underlying graph; calling it on the filtered_graph
> does the same thing. Does your random_int() function re-seed the RNG to get
> a different answer each time?
> I think overall that your code is nearly ready to put in. What did you
> want me to do with the file? Put that in the documentation
> somewhere, or is most of the content in there about building it outside
> Boost (where it will build with the rest of the BGL examples using
> Boost.Build)?
> -- Jeremiah Willcock
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