% Problem # 3 (Shubert's, Trigonometric Polynomial, or Suharev-Zilinskas' Function)
% Range of initial points: -10 <= x <= 10
% It has three global maximum: x={-6.77457614347361, -0.491390835930674,
% 5.79179447080188}
% f(x)=12.031249442167146
% Coded by: Ali R. Alroomi | Last Update: 04 March 2015 | www.al-roomi.org
 
clear
clc
warning off
 
xmin=-10;
xmax=10;
R=100000; % steps resolution
x=xmin:(xmax-xmin)/R:xmax;
    
for i=1:length(x)
    
    for j=1:5
        fs(j)=j*sin((j+1)*x(i)+j);
    end
    
    f(i)=sum(fs);
 
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');