Issue with getHeadOfTheEdge() and getTailOfTheEdge() methods

[atulpundir88]

The methods - getHeadOfTheEdge() and getTailOfTheEdge() defined in ColouredGraph class do not always return the head and tail of the edge.

For example, Consider the outgoing edges for a specific vertex. The tail of all such edges should always be the specific vertex, while the head can be some other vertex. However, different behaviour can be observed.

For the below code, the expected output is not displayed.
IntSet outEdges = graph.getOutEdges(2);
System.out.println("Outgoing Edges: " + outEdges);
for(int edge: outEdges) {
System.out.println("Head: " + graph.getHeadOfTheEdge(edge));
System.out.println("Tail: " + graph.getTailOfTheEdge(edge));
System.out.println("--");
}

Output :
Outgoing Edges: {1, 3, 2, 4}
Head: 2
Tail: 1

Head: 3
Tail: 2

Head: 3
Tail: 2

Head: 2
Tail: 1

Expected: Tail should always be 2.

Link for complete test case : https://github.com/UPB-Lemming-Group/Lemming/blob/optimize_expressions/src/test/java/org/aksw/simba/lemming/metrics/single/updateDegree/TripleIssue.java
Input File used : https://github.com/UPB-Lemming-Group/Lemming/blob/optimize_expressions/src/test/resources/expressions_max_test.n3
Triple Issue.pdf