Re: Weight as a function of distance at source

From: Alex Hagen-Zanker (a.hagen-zanker_at_[hidden])
Date: 2020-12-18 09:35:08

>>In a way, yes. But I don't see where dijkstra would fail here given the weights are always positive. A regular bfs from a given start time should populate the distances to all nodes, identical to dijkstra

I think you are right, as long as you cannot get a better connection by arriving later.

The combine function is supposed to combine a distance and a weight, typically these are the same type. Perhaps you are better off incorporating the waiting time in your weight property map.

You might be able to do this using the function_property_map (https://www.boost.org/doc/libs/1_59_0/libs/property_map/doc/function_property_map.html ).

Or to create your own property map, similar to this:

template<class G, class DistanceMapType, class TravelTimeMapType>
class weightmap
{
  using distance_type = int;
  using weight_type = int;

public:
  using key_type = Edge<G>;
  using value_type = weight_type;
  using reference = weight_type;
  using category = boost::readable_property_map_tag;


  weight_type get(const Edge<G>& e) const
  {
    weight_type travel = get(travel_time_map,e);
    distance_type distance = get(distance_map, boost::source(e));
    weight_type wait = 60 - distance % 60; // assuming hourly service
    return travel + wait;
  }

private:
  DistanceMapType distance_map;        // total time to each vertex
  TravelTimeMapType travel_time_map;   // time to travel over each edge
};

template<class G>
int get(const weightmap<G>& w, const Edge<G>& e)
{
  return w.get(e);
}.



On Fri, Dec 18, 2020 at 6:39 AM Alex Hagen-Zanker <a.hagen-zanker_at_[hidden]<mailto:a.hagen-zanker_at_[hidden]>> wrote:
>My actual use case is where weights represent nodes in a transport system and for a person arriving at a vertex at some time Tx, there is a variable weight of using the next outbound transport = waiting_time + travel_time, where waiting_time is a function of Tx.

That sounds like you intend to calculate a *dynamic* shortest path, which is not what Dijkstra's algorithm does for you.

I know it doesn't answer your question, but I think it is more pertinent.

Kind regards, Alex