function z=peaksfun(x1,x2)
% >> peaks;  % Peaks formula
x=x1; y=x2;
z =  3*(1-x).^2.*exp(-(x.^2) - (y+1).^2) ... 
   - 10*(x/5 - x.^3 - y.^5).*exp(-x.^2-y.^2) ... 
   - 1/3*exp(-(x+1).^2 - y.^2) ;