a11 a12 Cll C In C21c22 lmI lm =a1b1;+a12b2+…+anb 11C12 In 21C 22 n i1 i2 n n              m m m n ij n n c c c c c c c c c c       1 2 21 22 2 11 12 1                         = rj j j i i i r b b b a a a   2 1 1 2