12 21心22 2 m1 bm2 mm Sn=S2=∑(x-x,)(n=1) Sk=∑(x2-xxn-X)S = S11 S12 … S1m S21 S22 … S2m     Sm1 Sm2 … Smm   / 1 1 2 2      S S X X n n i jj j ij i   / 1 1      S X X X X n n i jk ij j ij k