% Strongin's Function
% Range of initial points: -1.5 <= x <= 4.5
% Global minima: x=0
% f(x)=0
% Coded by: Ali R. Alroomi | Last Update: 18 Jan. 2015 | www.al-roomi.org
 
clear
clc
warning off
 
xmin=-1.5;
xmax=4.5;
R=100000; % steps resolution
x=xmin:(xmax-xmin)/R:xmax;
    
for i=1:length(x)
    f(i)=2-cos(x(i))-cos(2*x(i));
end
 
plot(x,f,'r','LineWidth',2);grid;set(gca,'FontSize',12);
xlabel('x','FontName','Times','FontSize',20,'FontAngle','italic');
ylabel('f(x)','FontName','Times','FontSize',20,'FontAngle','italic');