西安毛子科技大学XIDIAN UNIVERSITYx2a*, ++a*+jl-(xax) =Ca,xixjV-i=l j=1f(xI,X2....x,)= X'AX于是有于是有 1 2 ( , ,..., ) . n f x x x X AX =  1 1 2 2 1 1 1 n n n j j j j n nj j j j j x a x x a x x a x = = = = + + +    1 1 ( ) n n i ij j i j x a x = = =   1 1 n n i j ij i j a x x = = =  