f(x1,x2,x3)=(x1-x2)^2+(x2-x3)^2=x1^2 - 2x1x2 + 2x2^2 - 2x2x3 + x3^2A = 1 -1 0-1 2 -1 0 -1 1
[x1 x2 x3][1 -1 0 ; -1 2 -1 ; 0 -1 1][x1 x2 x3]T
