I don't know if it helps:
%%main func
clear all;
close all;
clf;
clc;
% Define the function
x = linspace(-10,10,100);
f = @Goldenfunc;
y = f(x);
figure(1)
plot(x,y,'k',LineWidth=2), hold on
xr = GoldenSection(0,10,f);
plot(xr,'bo')
function [xr] = GoldenSection(xL,xU,y)
N = 200;
GR = (sqrt(5)-1) / 2; % Golden Ratio Number
d = GR * (xU-xL);
x1 = xL + d;
x2 = xU - d;
fx1 = y(x1); % y(x1) alamıyor çünkü x1 positive integer değil
fx2 = y(x2);
for i=1:N
if fx1 > fx2 % Move lower bound to x1
xL = x1;
fL = fx1;
x1 = x2; % update x1
fx1 = fx2;
d = GR * (xU - xL); %update d & x2
x2 = xL + d;
fx2 = y(x2);
elseif fx1 < fx2
xU = x2;
fU = fx2;
x2 = x1;
fx2 = fx1;
d = GR * (xU - xL); %update d & x1
x1 = xU - d;
fx1 = y(x1);
else
xL = (x1 + x2) / 2;
xU = xL;
end
end
xr = (x1 + x2) / 2;
%plot(xr,'ko')
end
function y = Goldenfunc(x)
%x = linspace(0,10,100);
y = x.^2 - 6*x + 15;
%plot(x,y);
%hold on
end
