PageRank Algorithm

Computer Science: OCR A Level, topic 3.4.5

PageRank Algorithm

The PageRank algorithm is a method of ranking the web pages in a set of Google search results.

PageRank algorithm

PageRank is named after Larry Page who, along with fellow Stanford University student Sergey Brin, developed the algorithm in the mid-1990s.
The algorithm judges how important each web page is.
The higher the score for a particular page, the closer to the top of the list of results it appears.

Operation

Google searches often contain millions of results, so PageRank is an important method of ensuring useful pages are more prominent in the list.
The algorithm has to be run constantly for each web page as the number of external links to the page can change at any time.

Algorithm

Algorithm

The PageRank algorithm is written as follows:
$PR(A) = (1-d) + d \left(\frac{PR(T_1)}{C(T_1)} + ... + \frac{PR(T_n)}{C(T_n)}\right)$
Using ‘Web page A’ as an example:
$PR(A)$ is to the PageRank of ‘Web page A’.
$PR(T_i)$ is the PageRank of any of $n$ pages which link to ‘Web page A’.
$C(T_i)$ is the number of outbound links on the pages which link to ‘Web page A’.
$d$ is the damping factor, which is usually set to 0.85.

Test yourself on PageRank Algorithm

What order of magnitude of results do most google searches return?

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