x=linspace(-3,3,40);
y=linspace(-3,3,40);
[x,y]=meshgrid(x,y);
z=-x.*y.*exp(-x.^2-y.^2); %z=f(x,y)
contour(x,y,z,20); 
grid on
axis equal
axis tight
xlabel('x-axis')
ylabel('y-axis')
title('Level curves of the function f(x,y).')