/// <summary>
/// Calculate a PageRank object's PageRank Score using the formula provided by Google's founders Larry Page and Sergey Brin.
/// This algorithm corresponds with the algorithm originally created by Massimo Marchiori and also is defined as a Markov Chain.
/// </summary>
/// <param name="pr">PageRank object</param>
/// <returns></returns>
private double CalculatePageRankScore(PageRank pr)
{
double left = (1 - this.m_Damper);
int outgoingLinkAmount = pr.OutgoingLinkCount;
if (outgoingLinkAmount > 0)
{
return(left + this.m_Damper * (pr.Score / outgoingLinkAmount));
}
return(left);
}
/// <summary>
/// Do the iterative calculation of the graph's pages PageRank score.
/// Hide this from the consumer of this class.
/// </summary>
/// <param name="_graph">A directed graph object</param>
/// <param name="_damping">A value between 0 and 1</param>
private void CalculatePageRank(IGraph _graph, double _damping = 0.85)
{
// Make sure it's within the bounds: 0 <= d <= 1
if (_damping < 0 || _damping > 1)
{
_damping = m_Damper;
}
// Create initial page rankings
foreach (IEdge <WebPageInfo> edge in _graph.Edges)
{
// We only need to process any URL once...
// Therefore if only add a URL to the PageRankList if it's not in the list!
if (!this.PageRankList.Any <PageRank>((PageRank prs) => Helper.IsUriSame(prs.Url, edge.Source.Url)))
{
this.PageRankList.Add(edge.Source);
}
// Same with target URL's
if (!this.PageRankList.Any <PageRank>((PageRank prt) => Helper.IsUriSame(prt.Url, edge.Target.Url)))
{
this.PageRankList.Add(edge.Target);
}
}
double tempTotal = 0.0;
Boolean isDone = false;
// Iterate until isDone is satisfied (TotalScore >= 1.0)
while (!isDone)
{
for (int i = 0; i < this.PageRankList.Count; i++)
{
PageRank pr = this.PageRankList[i];
Debug.Assert(!Double.IsNaN(pr.Score)); // Make sure it's a number
pr.Score = CalculatePageRankScore(pr); // Update the PageRank Score
tempTotal += pr.Score; // TotalScore;
}
isDone = tempTotal >= 1.0; // Done yet?
if (isDone)
{
// If done, then save the temporary total score in the global instance variable
TotalScore = tempTotal;
}
tempTotal = 0; // Reset temporary total score for this iteration!
IterationCount++; // Increment by 1 after each iteration
}
}
