% Problem # 9 (Timonov's Function # 3 or Zilinskas' Function # 1)
% Range of initial points: 3.1 <= x <= 20.4
% Global maxima: x=17.039198942112002
% f(x)=1.905961118715785
% Coded by: Ali R. Alroomi | Last Update: 14 Feb. 2015 | www.al-roomi.org
 
clear
clc
warning off
 
xmin=3.1;
xmax=20.4;
R=100000; % steps resolution
x=xmin:(xmax-xmin)/R:xmax;
    
for i=1:length(x)
    f(i)=-sin(x(i))-sin(2*x(i)/3);
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');