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"A Comparative Study of Language Support for Generic Programming" used a sample of the Boost Graph Library to compare the generic programming techniques available in C++, ML, Haskell, Eiffel, Java Generics, Generic C# (Source code). These Nice implementations use parameterised interfaces to represent most concepts (a few are represented by functions).

The generic algorithms BreadthFirstSearchExample, DijkstraShortestPathsExample, PrimMinimumSpanningTreeExample, BellmanFordShortestPathsExample, and JohnsonAllPairsShortestPathsExample, make use of GraphConceptsExample and GraphClassesExample and GraphTestExample.

Bellman Ford Shortest Paths

package graph;

<Vertex, Edge, Distance, T | Edge <: GraphEdge<Vertex> > 
boolean bellmanFordShortestPaths(
   EdgeListGraph<Vertex,Edge> graph,
   int size,
   ReadablePropertyMap<Edge,Distance> weightMap,
   ReadWritePropertyMap<Vertex,Vertex> predecessor,
   ReadWritePropertyMap<Vertex,Distance> distance,
   (Distance, Distance)->Distance combine,
   (Distance, Distance)->boolean compare
   ){
   
   for (int i = 0; i < size; ++i) {
      boolean anyRelaxed = false; // Optimization from BGL
      for ( Edge edge : graph.edges )
         if( relax(edge, weightMap, distance, predecessor, combine, compare) )
            anyRelaxed = true; 
                       
      if (!anyRelaxed) break;
   }

   for ( Edge edge : graph.edges() )
      if (compare( 
         combine(weightMap[edge], distance[edge.source]), 
         distance[edge.target])
         )
            return false;

   return true;
}


void bellmanFordTest(){ 
   AdjacencyList <int, AdjacencyListEdge<int>> g = simpleGraph(); 
   HashPropertyMap<int, double> distanceMap = simpleDistanceMap();  
   HashPropertyMap<AdjacencyListEdge<int>, double> weightMap = negativeWeights();    
   
   HashPropertyMap<int, int> predMap = new HashPropertyMap();  
    
   bellmanFordShortestPaths(
      g, 
      4,
      weightMap,
      predMap,
      distanceMap,
      (double a, double b) => { return a + b; },
      (double a, double b) => { return a < b; }
      );

   for (i : 3..6) {
      print("Dist(" i ")="   distanceMap.get(i));                     
      print(", Pred(" i ")=");
      
      // Maybe a Vertex has no predecessors? 3
      try { print( predMap.get(i) ); 
      } catch (NoSuchElementException ex){}    
        
      println("");
   }
}

Test Results

(For tests in GraphTestExample.)
Breadth First Search Test
=========================
initialize 3
initialize 4
initialize 5
initialize 6
discover 3
discover 3
examine edge(3 -> 6)
tree edge(3 -> 6)
examine edge(3 -> 5)
tree edge(3 -> 5)
finish 3
discover 6
examine edge(6 -> 4)
tree edge(6 -> 4)
finish 6
discover 5
finish 5
discover 4
examine edge(4 -> 5)
nontree edge(4 -> 5)
black target edge(4 -> 5)
examine edge(4 -> 3)
nontree edge(4 -> 3)
black target edge(4 -> 3)
finish 4

Dijkstra Shortest Paths Test
============================
Dist(3)=0.0, Pred(3)=3
Dist(4)=7.0, Pred(4)=6
Dist(5)=8.0, Pred(5)=3
Dist(6)=5.0, Pred(6)=3

Prim Minimum Spanning Tree Test
===============================
Pred(3) = 3
Pred(4) = 6
Pred(5) = 4
Pred(6) = 3

Bellman-Ford Shortest Paths Test
================================
Dist(3)=0.0, Pred(3)=
Dist(4)=3.0, Pred(4)=6
Dist(5)=2.0, Pred(5)=4
Dist(6)=5.0, Pred(6)=3

Johnson All-Pairs Shortest Paths Test
=====================================
3: 0.0 3.0 2.0 5.0
4: 3.0 0.0 -1.0 8.0
5: Infinity Infinity 0.0 Infinity
6: 1.0 -2.0 -3.0 0.0

-- IsaacGouy - 07 Jan 2004

Topic GraphParametricTypeExample . { Edit | Attach | Ref-By | Printable | Diffs | r1.8 | > | r1.7 | > | r1.6 | More }
Revision r1.3 - 20 Jan 2004 - 05:31 GMT - IsaacGouy
Parents: WebHome > CodeExamples
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