以a+b近似表达时的均方误差为 E[n-(a2+b)]2 =El(n-En-as-E5+(En-aE5-b)12 E[(n-Em)2+a2(2E2)2+(EaEb)2 2a(n-Ens-E$+2(n-Enen-aEs-b 2a(s-Es(En-aE5-b)] -E(n-En2+aE(S-E52+(en-aE5-b)2 2aE(-En(s-esI 为了表达方便,令 (5,) E[(-Em)-E) ()o() 9 2021/2/202021/2/20 9 以ax+b近似表达h时的均方误差为 E[h-(ax+b)]2 =E[(h-Eh)-a(x-Ex)+(Eh-aEx-b)]2 =E[(h-Eh) 2+a 2 (x-Ex) 2+(Eh-aEx-b) 2 -2a(h-Eh)(x-Ex)+2(h-Eh)(Eh-aEx-b) -2a(x-Ex)(Eh-aEx-b)] =E(h-Eh) 2+a 2E(x-Ex) 2+(Eh-aEx-b) 2 -2aE[(h-Eh)(x-Ex)]. 为了表达方便, 令 [( )( )] ( , ) . (1) ( ) ( ) E E E h h x x  x h s x s h - - =