http://jung.sourceforge.net/
https://github.com/louridas/pagerank/blob/aeb9b17ada1f925bb525961574f6d8736742f47f/java/PageRankCalc.java
加权的pagerank
https://github.com/jrtom/jung/blob/master/jung-algorithms/src/test/java/edu/uci/ics/jung/algorithms/scoring/TestPageRank.java
http://linhaoxiang.iteye.com/blog/2038523