% Goldstein-Price's Function
% Range of initial points: -2 < xj < 2 , j=1,2
% Global minima: (x1,x2)=(0,-1)
% f(x1,x2)=3
% Coded by: Ali R. Alroomi | Last Update: 24 March 2015 | www.al-roomi.org
    
clear
clc
warning off
    
x1min=-2;
x1max=2;
x2min=-2;
x2max=2;
R=1500; % steps resolution
x1=x1min:(x1max-x1min)/R:x1max;
x2=x2min:(x2max-x2min)/R:x2max;   
    
for j=1:length(x1)
        
    for i=1:length(x2)              
        u(i)=1+((x1(j)+x2(i)+1).^2)*(19-14*x1(j)+3*x1(j).^2-14*x2(i)+6*x1(j)*x2(i)+3*x2(i).^2);
        v(i)=30+((2*x1(j)-3*x2(i)).^2)*(18-32*x1(j)+12*x1(j).^2+48*x2(i)-36*x1(j)*x2(i)+27*x2(i).^2);
        f(i)=u(i)*v(i);
    end
        
    f_tot(j,:)=f/(3*10^5);

end

figure(1)
meshc(x1,x2,f_tot);colorbar;set(gca,'FontSize',12);
xlabel('x_2','FontName','Times','FontSize',20,'FontAngle','italic');
set(get(gca,'xlabel'),'rotation',25,'VerticalAlignment','bottom');
ylabel('x_1','FontName','Times','FontSize',20,'FontAngle','italic');
set(get(gca,'ylabel'),'rotation',-25,'VerticalAlignment','bottom');
zlabel('f(X)','FontName','Times','FontSize',20,'FontAngle','italic');
title('3D View','FontName','Times','FontSize',24,'FontWeight','bold');

figure(2)
mesh(x1,x2,f_tot);view(0,90);colorbar;set(gca,'FontSize',12);
xlabel('x_2','FontName','Times','FontSize',20,'FontAngle','italic');
ylabel('x_1','FontName','Times','FontSize',20,'FontAngle','italic');
zlabel('f(X)','FontName','Times','FontSize',20,'FontAngle','italic');
title('X-Y Plane View','FontName','Times','FontSize',24,'FontWeight','bold');

figure(3)
mesh(x1,x2,f_tot);view(90,0);colorbar;set(gca,'FontSize',12);
xlabel('x_2','FontName','Times','FontSize',20,'FontAngle','italic');
ylabel('x_1','FontName','Times','FontSize',20,'FontAngle','italic');
zlabel('f(X)','FontName','Times','FontSize',20,'FontAngle','italic');
title('X-Z Plane View','FontName','Times','FontSize',24,'FontWeight','bold');

figure(4)
mesh(x1,x2,f_tot);view(0,0);colorbar;set(gca,'FontSize',12);
xlabel('x_2','FontName','Times','FontSize',20,'FontAngle','italic');
ylabel('x_1','FontName','Times','FontSize',20,'FontAngle','italic');
zlabel('f(X)','FontName','Times','FontSize',20,'FontAngle','italic');
title('Y-Z Plane View','FontName','Times','FontSize',24,'FontWeight','bold');