% Problem # 17 (or Lévy's Function # 1)
% Range of initial points: -4 <= x <= 4
% Two global maxima: x={-3,3}
% f(x)=-7
% Coded by: Ali R. Alroomi | Last Update: 06 July 2015 | www.al-roomi.org
 
clear
clc
warning off
 
xmin=-4;
xmax=4;
R=100000; % steps resolution
x=xmin:(xmax-xmin)/R:xmax;
 
for i=1:length(x)
    f(i)=-x(i)^6+15*x(i)^4-27*x(i)^2-250;
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');