/// <summary>
/// Compute the condensation graph and store it in the supplied graph 'cg'
/// </summary>
/// <param name="cg">
/// Instance of mutable graph in which the condensation graph
/// transformation is stored
/// </param>
public void Create(IMutableVertexAndEdgeListGraph cg)
{
if (cg == null)
{
throw new ArgumentNullException("cg");
}
if (components == null)
{
ComputeComponents();
}
// components list contains collection of
// input graph Vertex for each SCC Vertex_ID
// (i.e Vector< Vector<Vertex> > )
// Key = SCC Vertex ID
sccVertexMap = BuildSCCVertexMap(components);
// Lsit of SCC vertices
VertexCollection toCgVertices = new VertexCollection();
IDictionaryEnumerator it = sccVertexMap.GetEnumerator();
while (it.MoveNext())
// as scc_vertex_map is a sorted list, order of SCC IDs will match CG vertices
{
IVertex curr = cg.AddVertex();
OnInitCondensationGraphVertex(new CondensationGraphVertexEventArgs(curr, (IVertexCollection)it.Value));
toCgVertices.Add(curr);
}
for (int srcSccId = 0; srcSccId < sccVertexMap.Keys.Count; srcSccId++)
{
VertexCollection adj = new VertexCollection();
foreach (IVertex u in (IVertexCollection)sccVertexMap[srcSccId])
{
foreach (IEdge e in VisitedGraph.OutEdges(u))
{
IVertex v = e.Target;
int targetSccId = components[v];
if (srcSccId != targetSccId)
{
// Avoid loops in the condensation graph
IVertex sccV = toCgVertices[targetSccId];
if (!adj.Contains(sccV)) // Avoid parallel edges
{
adj.Add(sccV);
}
}
}
}
IVertex s = toCgVertices[srcSccId];
foreach (IVertex t in adj)
{
cg.AddEdge(s, t);
}
}
}
/// <summary>
/// Adds temporary edges to the graph to make all vertex even.
/// </summary>
/// <param name="g"></param>
/// <returns></returns>
public EdgeCollection AddTemporaryEdges(IMutableVertexAndEdgeListGraph g)
{
if (g == null)
{
throw new ArgumentNullException("g");
}
// first gather odd edges.
VertexCollection oddVertices = AlgoUtility.OddVertices(g);
// check that there are an even number of them
if (oddVertices.Count % 2 != 0)
{
throw new Exception("number of odd vertices in not even!");
}
// add temporary edges to create even edges:
EdgeCollection ec = new EdgeCollection();
bool found, foundbe, foundadjacent;
while (oddVertices.Count > 0)
{
IVertex u = oddVertices[0];
// find adjacent odd vertex.
found = false;
foundadjacent = false;
foreach (IEdge e in g.OutEdges(u))
{
IVertex v = e.Target;
if (v != u && oddVertices.Contains(v))
{
foundadjacent = true;
// check that v does not have an out-edge towards u
foundbe = false;
foreach (IEdge be in g.OutEdges(v))
{
if (be.Target == u)
{
foundbe = true;
break;
}
}
if (foundbe)
{
continue;
}
// add temporary edge
IEdge tempEdge = g.AddEdge(v, u);
// add to collection
ec.Add(tempEdge);
// remove u,v from oddVertices
oddVertices.Remove(u);
oddVertices.Remove(v);
// set u to null
found = true;
break;
}
}
if (!foundadjacent)
{
// pick another vertex
if (oddVertices.Count < 2)
{
throw new Exception("Eulerian trail failure");
}
IVertex v = oddVertices[1];
IEdge tempEdge = g.AddEdge(u, v);
// add to collection
ec.Add(tempEdge);
// remove u,v from oddVertices
oddVertices.Remove(u);
oddVertices.Remove(v);
// set u to null
found = true;
}
if (!found)
{
oddVertices.Remove(u);
oddVertices.Add(u);
}
}
temporaryEdges = ec;
return(ec);
}
