This picture is from the patent for Google's search algorithm, PageRank. It describes in simple terms how the algorithm works.
- A, with PageRank 0.4, has two links out, to B and C, so contributes half of its PageRank to each of those - 0.2.
- B has rank 0.2, since A is the only incoming link. B links to C, contributing 0.2. Combined with the link from A, C has PageRank 0.4.
- A has one incoming link, from C. This is C's only outgoing link, so contributes 0.4, C's PageRank, to A.
The circular logic is spell-binding.