Bellman-Ford Query

["Acarali, Dilara" <Dilara.Acarali AT city.ac.uk>]

Hello, 

I've been using GraphStream, and specifically exploring the Bellman-Ford algorithm implementation to find distance between nodes on a simple graph.  I run the algorithm and print the results as follows:

connection  length  path      

1->1        0.0     []        

1->2        1.0     [2, 1]    

1->3        2.0     [3, 2, 1] 

1->4        1.0     [4, 1]    

1->5        2.0     [5, 4, 1] 

1->6        1.0     [6, 1]    

 

2->1        0.0     []        

2->2        0.0     []        

2->3        1.0     [3, 2]    

2->4        1.0     [4, 1]    

2->5        2.0     [5, 3, 2] 

2->6        1.0     [6, 2]    

3->1        0.0     []        

3->2        1.0     [2, 1]    

3->3        0.0     []        

3->4        1.0     [4, 1]    

3->5        1.0     [5, 3]    

3->6        1.0     [6, 3]    

The code I use looks like this:

for (Node srcNode : graph.getEachNode()) {

   BellmanFord presimBellman = new BellmanFord("hops", srcNode.getId());

   presimBellman.init(graph);

   presimBellman.compute();

for (Node dstNode : graph.getEachNode()) {

String connection = "" + srcNode.getId() + "->" + dstNode.getId();

double pathLength = presimBellman.getShortestPath(dstNode).getNodeCount();

Path path = presimBellman.getShortestPath(dstNode);

          }

}

My question is, why does 1->2 return the correct hop count of 1, but 2->1 does not? I tried setting both node1 and node2 as the source node in the Bellman-Ford constructor (on alternative runs) and still get the same result. I am aware that this is a stub implementation but don't think this should be happening? 

I also get the same result when I run:

BellmanFord testBellman = new BellmanFord("hops", "2");

testBellman.init(graph);

testBellman.compute();

System.out.println(testBellman.getSource() + "->1 = " + testBellman.getShortestPathValue(1));

Any feedback would be much appreciated.

Regards

Dilara