PageRank

PageRank is a link analysis algorithm, developed by Larry Page and Sergey Brin (Google), that gives each web page a numerical score of its importance based on the number and quality of pages linking to it. A link from page A to B is counted as a vote for B, and a vote from an important page counts more.

Formula

PR(A) = (1 - d) + d × ( PR(T1)/C(T1) + PR(T2)/C(T2) + ... + PR(Tn)/C(Tn) )

• T1...Tn are pages that link to A.
• C(Ti) is the number of outgoing links on Ti.
• d is the damping factor, usually 0.85, the probability that a user keeps following links; (1 - d) represents a random jump.

Notes

• It is computed iteratively until values converge.
• It can be seen as the probability that a random surfer lands on the page.
• It is used with many other factors (content relevance) to rank search results.

Example

If page A is linked by B (PR 1, 2 out-links) and C (PR 1, 1 out-link), then PR(A) = 0.15 + 0.85 × (1/2 + 1/1) = 1.425.