Re: [Boost-users] [Boost Graph] newbie - dijkstra & external weightmap

Subject: Re: [Boost-users] [Boost Graph] newbie - dijkstra & external weightmap
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2009-12-15 10:40:53

> Thanks Jeremiah,
>
> But I'm talking about edge weights - why would you put in 
> "get(vertex_index,g)" and not "get(edge_index,g)" or similar (I've tried this 
> simple substitution and it doesn't work; so it's obviously more complex than 
> that)?

OK.  I misread that -- you do want edge_index.  You will need to provide 
them yourself, though.  You must have some mapping from edges to numbers 
already to index the vector; that needs to be turned into a property map.

> In any case I've tried more or less exactly what you suggested as 
> follows but the compiler spits out a long error, reported below 
> (libboost1.40):
>
> --------
> #include <boost/property_map/property_map.hpp>
> class road;
> typedef adjacency_list<setS,vecS,undirectedS,no_property,road> Graph;
> typedef boost::vertex_descriptor vdest;
> vdest shortest_path(Graph& g, vdest src, vdest dst)
>  {
>  vector<vdest> parent(num_vertices(g));
>  vector<double> agent_weightmap(num_edges(g));
>
>  dijkstra_shortest_paths(g,src,
>    //weight_map(get(&road::transit_time,g))   // ---> this weight_map works
>    weight_map(make_iterator_property_map(agent_weightmap.begin(), 
> get(vertex_index, g)))
>    .predecessor_map(make_iterator_property_map(parent.begin(), 
> get(vertex_index, g))));
>
>  vdest vd;
>  for (vd=dst ; parent[vd]!=src ; vd=parent[vd]);
>  return(vd);
>  }
> --------
>
>
> Compiler error:
> -------
> /usr/include/boost/property_map/property_map.hpp: In function ‘Reference 
> boost::get(...
> [lots of instantiated froms] ...
> instantiated from [dijkstra_shortest_paths(...)]
> /usr/include/boost/property_map/property_map.hpp:317: error: no match for 
> ‘operator[]’ in ‘(const 
> boost::iterator_property_map<__gnu_cxx::__normal_iterator<double*,  ....
> /usr/include/boost/property_map/property_map.hpp:354: note: candidates are: R 
> boost::iterator_property_map<RandomAccessIterator, IndexMap, .......
> -------
>
> I'm getting a backward warning on hash_set included from 
> boost/graph/adjacency_list.hpp - could this be an issue?

The warning is not interesting -- it's just saying that BGL is using 
old-style hash tables; 1.41 (I believe) has this fixed.  I do not know the 
exact cause of the operator[] error; you removed too much of the error 
message to tell.

-- Jeremiah Willcock