[codeface] Re: Page rank numerical stability issues
- From: Wolfgang Mauerer <wm@xxxxxxxxxxxxxxxx>
- To: codeface@xxxxxxxxxxxxx
- Date: Mon, 04 Aug 2014 20:19:53 +0200
Hi Mitchell,
Am 04/08/2014 19:27, schrieb Mitchell Joblin:
There are numerical stability issues with computing the page rank using
old igraph packages. The page rank algorithm is iterative and under
certain matrix conditions the max iteration threshold is met before the
algorithm is able to converge on the solution. One can check if the
maximum number of iterations was met by looking at the options
parameters. The problem is manifested as extremely large or negative
page rank values. The page rank values represent the probability of
visiting a node (on a random walk plus a teleport operation) which means
the sum of page rank values over all nodes should equal 1. This is also
a good test to see if the page rank algorithm functioned correctly.
With the latest version of igraph it seems that these numerical problems
no longer occur. I suggest anyone experiencing strange page rank values
to upgrade to igraph-0.7.
thanks for the analysis and the information -- does that solve
the oddities we've seen with some recent 3.x Linux kernel releases?
Thanks, Wolfgang
Kind regards,
Mitchell Joblin
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