[x1,x2] = meshgrid(-5:0.1:5);
f=-20*exp(-0.2*sqrt(0.5*(x1.^2+x2.^2)))-exp(0.5*(cos(2*pi*x1)+cos(2*pi*x2)))+22.71282;
mesh(x1,x2,f); 
xlabel('x1');
ylabel('x2');
zlabel('f(x1,x2)');