clc;
clear;

a = 20;
b = 0.2;
c = 2*pi;
n = 2;

[x,y] = meshgrid(-5:0.2:5, -5:0.2:5);

z =( -a*exp(-b*sqrt((1/n)*(x.^2+y.^2)))-exp((1/n)*(cos(c*x) + cos(c*y))));
% = x.^2 + x.*y - 0.5.*y.^2 - x - y;
%fun = @(x)(x(1)^2 + x(1)*x(2) - 0.5*x(2)^2 -x(1) -x(2));


figure(1)

V = -30:1:30;
[C,h] = contour(x,y,z,V);
grid on;
set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2)

figure(2)
surf(x,y,z)

tolx=10^-12;
tolfun=10^-1;
options=optimset('PlotFcns',@optimplotfval,'TolX', tolx);

fun = @(x)(-a*exp(-b*sqrt((1/n)*(x(1).^2+x(2).^2)))-exp((1/n).*(cos(c.*x(1)) + cos(c.*x(2)))));
%fun = @(x)(x(1).^2 + x(1).*x(2) - 0.5.*x(2).^2 -x(1) -x(2));
x0=[-6,8];

[x,fval,exitflag,output, grad, hessian]=fminunc(fun,x0,options)
V = -30:1:30;
[C,h] = contour(x,y,z,V);
grid on;
set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2)