PageRank is defined as the stationary state of a Markov chain. The chain is obtained by perturbing the transition matrix induced by a web graph with a damping factor $alpha$ that spreads uniformly part of the rank. The choice of $alpha$ is eminently empirical, and in most cases the original suggestion $alpha=0.85$ by Brin and Page is still used. In this paper, we give a mathematical analysis of PageRank when $alpha$ changes. In particular, we show that, contrarily to popular belief, for real-world graphs values of $alpha$ close to $1$ do not give a more meaningful ranking. Then, we give closed-form formulae for PageRank derivatives of any order, and by proving that the $k$-th iteration of the Power Method gives exactly the PageRank value obtained using a Maclaurin polynomial of degree $k$, we show how to obtain an approximation of the derivatives. Finally, we view PageRank as a linear operator acting on the preference vector and show a tight connection between iterated computation and derivation.
@InProceedings{boldi_et_al:DagSemProc.07071.3, author = {Boldi, Paolo and Santini, Massimo and Vigna, Sebastiano}, title = {{A Deeper Investigation of PageRank as a Function of the Damping Factor}}, booktitle = {Web Information Retrieval and Linear Algebra Algorithms}, pages = {1--19}, series = {Dagstuhl Seminar Proceedings (DagSemProc)}, ISSN = {1862-4405}, year = {2007}, volume = {7071}, editor = {Andreas Frommer and Michael W. Mahoney and Daniel B. Szyld}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.07071.3}, URN = {urn:nbn:de:0030-drops-10722}, doi = {10.4230/DagSemProc.07071.3}, annote = {Keywords: PageRank, damping factor, Markov chains} }
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