PageRank. s1s1 p 12 p 21 s2s2 s3s3 p 31 s4s4 p 41 p 34 p 42 p 13 x 1 = p 21 p 34 p 41 + p 34 p 42 p 21 + p 21 p 31 p 41 + p 31 p 42 p 21 / Σ x 2 = p 31.
