Weight map as function in Boost Graph Dijkstra algorithm

Question

I\'m using Boost Graph Libraries and need to use a weightmap which is not constant, but which is a function of a parameter K (i.e. the edge costs depend on K). In practice,

Answer 1

There are a number of property map flavours. In particular one is the transform_value_property_map can be used here.

Simple Approach C++03

Assuming c++03 you'd write:

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#include <boost/property_map/transform_value_property_map.hpp>
#include <boost/bind.hpp>

// ...

boost::dijkstra_shortest_paths(g, a, boost::predecessor_map(&preds[0]).weight_map(
            boost::make_transform_value_property_map(
                boost::bind(&Edge::getWeight ,_1, 2), 
                boost::get(boost::edge_bundle, g))
        ));

Cleaner C++11

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auto wmap = make_transform_value_property_map([](Edge& e) { return e.getWeight(2); }, get(boost::edge_bundle, g));
boost::dijkstra_shortest_paths(g, a, boost::predecessor_map(&preds[0]).weight_map(wmap));

You can drop the boost/bind.hpp include.

Bonus: drop the getWeight() member function

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You don't actually need it. You could write a Phoenix actor in-place:

#include <boost/phoenix.hpp>
using boost::phoenix::arg_names::arg1;

auto wmap = make_transform_value_property_map(2 * (&arg1->*&Edge::weight), get(boost::edge_bundle, g));

Or use c++11 again:

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auto wmap = make_transform_value_property_map([](Edge& e) { return e.weight * 2; }, get(boost::edge_bundle, g));