public Vertex MergeVertices(int id1, int id2)
{
var v1 = Vertices.SingleOrDefault(e => e.Id == id1);
var v2 = Vertices.SingleOrDefault(e => e.Id == id2);
if (v1 == null)
{
throw new Exception($"Vertex '{id1}' not found");
}
if (v2 == null)
{
throw new Exception($"Vertex '{id2}' not found");
}
int maxId = Vertices.Select(e => e.Id).Max();
var merged = new Vertex(maxId + 1);
// add all neighbors
foreach (var neighbor in v1.Neighbors.ToList())
{
merged.AddNeighborBiDirection(neighbor);
}
foreach (var neighbor in v2.Neighbors.ToList())
{
merged.AddNeighborBiDirection(neighbor);
}
// remove old neighbor references from graph
foreach (var neighbor in v1.Neighbors.ToList())
{
v1.RemoveNeighborBiDirection(neighbor);
}
foreach (var neighbor in v2.Neighbors.ToList())
{
v2.RemoveNeighborBiDirection(neighbor);
}
merged.IdsBeforeMerge.AddRange(v1.IdsBeforeMerge);
merged.IdsBeforeMerge.AddRange(v2.IdsBeforeMerge);
Vertices.Remove(v1);
Vertices.Remove(v2);
Vertices.Add(merged);
return(merged);
}
/// <summary>
/// Generate graph by Holme & Kim model
/// </summary>
/// <param name="n">Number of vertices</param>
/// <param name="m0">Number of fundamental nodes</param>
/// <param name="m">Number of edges for new created vertices</param>
/// <para name="p">Probability of making a triad formation</para>
/// <returns></returns>
public Graph GenerateHolmeKimModel(int n, int m0, int m, double p)
{
var vertices = Enumerable.Range(0, m0).Select(id => new Vertex(id)).ToList();
// create base graph (complete graph)
for (int i = 0; i < m0; i++)
{
for (int j = 0; j < m0; j++)
{
if (i == j)
{
continue;
}
vertices[i].AddNeighborBiDirection(vertices[j]);
}
}
var vertexDegreeDistribution = new List <int>();
foreach (var vertex in vertices)
{
for (int i = 0; i < vertex.Degree; i++)
{
vertexDegreeDistribution.Add(vertex.Id);
}
}
// add new nodes
for (int i = m0; i < n; i++)
{
var vertex = new Vertex(m0 + i + 1);
var usedNodeIds = new List <int>();
Vertex newNeighbor = null;
for (int j = 0; j < m; j++)
{
if (j == 0 || p < _random.NextDouble())
{
int randomIndex = _random.Next(vertexDegreeDistribution.Count - 1);
while (usedNodeIds.Contains(vertexDegreeDistribution[randomIndex]))
{
randomIndex = _random.Next(vertexDegreeDistribution.Count - 1);
}
newNeighbor = vertices.Single(e => e.Id == vertexDegreeDistribution[randomIndex]);
bool isAdded = newNeighbor.AddNeighborBiDirection(vertex);
usedNodeIds.Add(vertexDegreeDistribution[randomIndex]);
}
else
{
if (newNeighbor == null)
{
throw new Exception();
}
var possibleNeighborsToAdd = newNeighbor.Neighbors.Except(new[] { vertex }).ToList();
var otherNeighbor = possibleNeighborsToAdd[_random.Next(possibleNeighborsToAdd.Count)];
vertex.AddNeighborBiDirection(otherNeighbor);
}
}
for (int j = 0; j < m; j++)
{
vertexDegreeDistribution.Add(vertex.Id);
vertexDegreeDistribution.Add(vertex.Neighbors[j].Id);
}
vertices.Add(vertex);
}
return(new Graph(vertices));
}
