clear all;clc;
syms x y
z=x^3*y^2-3*x*y^3-x*y+1;
dzdx2=diff(z,x,2);
dzdy2=diff(z,y,2);
dxy2=dzdx2+dzdy2;
figure(1);
ezsurf(z);
figure(2);
ezsurf(dxy2);