% Problem # 11 (or Marsden-Weinstein's Function)
% Range of initial points: -pi/2 <= x <= 2*pi
% Two global maximum: x={2.094395090000627,4.188790191441036}
% f(x)=1.5
% Coded by: Ali R. Alroomi | Last Update: 25 Feb. 2015 | www.al-roomi.org
 
clear
clc
warning off
 
xmin=-pi/2;
xmax=2*pi;
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');