Re: [Boost-users] BGL, shortest path between two nearby nodes in a huge graph

Subject: Re: [Boost-users] BGL, shortest path between two nearby nodes in a huge graph
From: Paolo Bolzoni (paolo.bolzoni.brown_at_[hidden])
Date: 2016-01-21 05:58:33

At the moment I was using the _no_color_map version (I have no
infinity edges), but the idea sounds fairly good.
Thanks a lot.

On Thu, Jan 21, 2016 at 7:50 PM, Daniel Hofmann <daniel_at_[hidden]> wrote:
> This exact use-case is described in the breadth_first_visit (note: not
> breadth_first_search) documentation:
>
>> Also, this difference allows for more flexibility in the color property map. For example, one could use a map that only implements a partial function on the vertices, which could be more space efficient when the search only reaches a small portion of the graph.
>
>>
> http://www.boost.org/doc/libs/1_60_0/libs/graph/doc/breadth_first_visit.html
>
> On 01/21/2016 10:06 AM, alex wrote:
>>> Dear list,
>>>
>>> I am a happy user of BGL, but recently I got stuck in a strange problem. I
>> think I
>>> am missing the obvious, so I'll be happy to read the fine manual if it's
>> the case.
>>> Just point me to the right direction.
>>>
>>> I need to find the shortest path between two nodes, for doing so I am
>> using
>>> dijkstra with a custom visitor that stops the search (throwing an
>> exception) when
>>> examine_vertex is called on the destination node.
>>>
>>> It worked fine, but it run strangely slow. After some profiling, it is
>> clear that
>>> most of the time is used in the initialize_vertex function.
>>> The graph is fairly large, but the path I am looking for are fairly small
>> (10 edges
>>> tops usually).
>>>
>>> It is possible to skip the initialize phase?
>>>
>>
>> There are a number of (undocumented)  dijkstra_shortest_paths_no_init(...)
>> functions in dijkstra_shortest_paths.hpp. I think you need the one with the
>> signature listed below, because it is the only one that does not initialize
>> the color map.
>>
>> A strategy can be to use a visitor to keep a list of all discovered vertices
>> and re-initialize those (predecessor, distance, color) after each path is
>> found.
>>
>> // Call breadth first search
>>   template <class Graph, class SourceInputIter, class DijkstraVisitor,
>>             class PredecessorMap, class DistanceMap,
>>             class WeightMap, class IndexMap, class Compare, class Combine,
>>             class DistZero, class ColorMap>
>>   inline void
>>   dijkstra_shortest_paths_no_init
>>     (const Graph& g,
>>      SourceInputIter s_begin, SourceInputIter s_end,
>>      PredecessorMap predecessor, DistanceMap distance, WeightMap weight,
>>      IndexMap index_map,
>>      Compare compare, Combine combine, DistZero zero,
>>      DijkstraVisitor vis, ColorMap color)
>>
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