Thanks for the help Tamas :-) Cheers, dksr
On Tue, Mar 19, 2013 at 4:21 PM, Tamás Nepusz <[email protected]> wrote: > Hi, > > > I am trying to compute pagerank for a graph and I am getting strange > values for pagerank. to my knowledge, the page rank values should be > between 0 and 1 but i get very large or very small number (> 1 and < 0). I > attach the .gml file and here is the output. Please let me know what I am > doing wrong or is this graph some strange special case? > So I've tried your code with an experimental branch of igraph which uses > the excellent PRPACK package to calculate PageRank scores instead of the > ARPACK solver. The good news is that it works flawlessly with your graph as > well as all our test cases. The not-so-good news is that it will make its > way into igraph 0.7 only. In the 0.6.5 version, I found that lowering the > damping value (i.e. increasing the teleportation probability during the > PageRank calculation) seemed to resolve the stability issues for your > particular graph; for instance, g.pagerank(damping=0.75) seems to work > reliably: > > >>> g = igraph.load(f) > >>> for i in xrange(1000): > ... pr = g.pagerank(damping=0.75) > ... if min(pr) < 0 or max(pr) > 1: > ... raise ValueError("bug") > ... > > The above code snippet runs fine for me, meaning that PageRank managed to > converge in all the 1000 executions. Note that changing the damping value > changes the value of all the PageRank scores, but the ordering of the nodes > should be the same (I guess). > > Best, > -- > Tamas > > > _______________________________________________ > igraph-help mailing list > [email protected] > https://lists.nongnu.org/mailman/listinfo/igraph-help >
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