x=linspace(-pi,pi,100);
y=x;
[X,Y]=meshgrid(x,y);
Z=cos(0.1+X.^2/5-X/3-Y/5+Y.^2/9);
Zmin=-cos(0.1+X.^2/5-X/3-Y/5+Y.^2/9);
surf(X,Y,Z)
