忽略高次项有: a1x1+b1x2(4) dt 2=a1x1+b1x2(5) dt 即 x1「a1b1TX1 a b,‖ 2 2 2 2 或写成:X=AX: X AX X X a b a b X X : (5) dt dx (4) dt dx , : 2 1 2 2 1 1 2 1 1 1 1 2 2 1 1 1 2 1 =             =         = + = +    或写成 即 忽略高次项有 a x b x a x b x