Check SimRank implementation

[rafguns]

Our current implementation is based on equations and an algorithm in Antonellis et al. (2008) (see Appendix A and Algorithm 1). While it yields fairly good results, it seems that this is not equal to SimRank as defined by Jeh and Widom (2002). Unit tests disagree with results obtained therein.

[rafguns]

Other SimRank implementations:

• In Perl: uses Jeh & Widom algorithm
• In C++: appears to use Antonellis algorithm
• In Python: uses Jeh & Widom algorithm but ironically yields still other results (see also this StackOverflow question and networkx-addon)

It is worth noting that Antonellis et al.'s algorithm is meant for bipartite click graphs. I should check whether it can be used for one-mode networks.

[rafguns]

Yet another implementation: https://github.com/amir-f/delta-simrank