Matrix multiplication iteratively.

I am new to matrix. While i know how to get r1 = (1/4, 1/8, 3/8, 1/4), I don't know how to get the r3 on ward.

Please show me the calculation.

System of Linear Equations Let X1,X2,X3,X4 be the PageRank scores (importance) of pages 1,2, 33 4, respectively. By multiplying MG with vector x = X1,X2,X3,X4 X1 1 2 3 4 X1 X2 1 0 0 0 1 X2 X3 = 2 i 0 0 0 X3 X4 3 5 1 0 0 X4 4 0 0 1 0 PageRank Algorithm We start with /0 = (1 1 1 1) (4) 4, 4, 4) and we iteratively compute at each step k > 1, rk = M. rk-1. We obtain