dijkstra_shortest_paths implicitly requires DistanceMap and WeightMap to be the same

[Luis G. Torres <lgtorres42@…>]

The documentation for dijkstra_shortest_paths states that the given distance_compare functor needs to be a BinaryPredicate where both arguments are of the value type of DistanceMap. The distance_combine functor needs to be a BinaryFunction where the first argument is of the DistanceMap value type and the second argument is of the WeightMap value type.

However, in line 162 of dijkstra_shortest_paths.hpp, a comparison is made between a value from WeightMap and a value from DistanceMap using the distance_compare functor; this violates where the documentation specifies that the distance_compare functor would only need to handle types from DistanceMap. Effectively, this requires either:

a) the value types of WeightMap and DistanceMap are made the same b) the distance_compare functor overloads operator() to have two different types of comparison

I imagine that fixing this issue would require either changing the documentation or changing line 162 to not require this comparison to be made (it seems to only be a way of verifying that there are no negative edges in the graph).

[Jeremiah Willcock]

(In [83772]) Changed test for negative edges per #8398; fixes #8398

[Jeremiah Willcock]

(In [85386]) Fixed test for negative-weight edges when combine operator is project2nd (as in prim_minimum_spanning_tree); fixes #9012; refs #8398