Q3: How does Googlerank webpages?Mung ChiangNetworks: Friends, Money, and Bytes
Webpages form a network Links in text: since mid-20th century… Hyperlinks in webpages Early 1990s: web, browser, portal… Mid to late 1990s: search… Directed graph Huge and sparse N=40—60 Billion webpages out there… And very few links in/out of most webpages
Which webpages are more important? Usefulness of ranking is hard to measure So rank by importance Quantify node importance: Count the number of links? More important links point to this page? Turn a seemingly cyclic statmeent to characterize an equilibrium of a recursive definition
General themesNetwork consists of Topology: graphs, matrices Functionality: what you do on the graphWe’ll see 3 matrices and a model of the “searchand navigation” functionality
Try 1Add up importance scores through incoming links
Try 2Normalize by the spread of importanceIs there a set of consistent scores?
Parallel with DPCBoth are special cases of “power method” usingnon-negative matrix theory
The challenge of scaleNumerical linear algebra methodsA few more tricks
SEOHow to increase your website rank?How Google reacts? Early 2011 May 2012
SummaryHyperlinked webpages form a networkConnectivity pattern provides a hint onimportancePagerank uniquely defines and efficientlycomputes a consistent set of importance scoresWhich can be viewed as the dominanteigenvector of the Google matrix
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