CODEWITHSUNDEEP
algorithmsearch-enginepagerank
lenhhoxung
lenhhoxung

Reputation: 2766

Calculate page rank

I'm learning PageRank algorithm and from Wikipedia, it gives the following formula:

enter image description here

From the formula, the page rank is calculated from the ranks of pages linking to it. Also, they give a simple example of four nodes A,B,C,D. Initially, each node has a page rank of 0.25. Therefore, if nodes B,C,D link to node A and there are no other links, PR(A) = 0.15 + 0.85*(0.25 + 0.25 + 0.25) = 0.7875 and PR(B) = PR(C) = PR(D) = 0.15. But the sum of page ranks is not equal to 1 which is the sum of ranks at the inital step. Am I wrong for this calculation?

I've read another tutorial, and in their calculation, the sum of ranks is always the same. Can anyone explain me where I'm wrong? Many thanks.

Upvotes: 1

Views: 1730

Answers (1)

kraskevich
kraskevich

Reputation: 18576

The formula that keeps the sum equal to 1 is (1 - d) / N + d * (...), not the one in your post (it's okay that the sum is not one with your formula). The Wikipedia article is clear about it:

The damping factor adjusts the derived value downward. The original paper, however, gave the following formula, which has led to some confusion:

... (your formula goes here)

The difference between them is that the PageRank values in the first formula sum to one, while in the second formula each PageRank is multiplied by N and the sum becomes N.

Upvotes: 1

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