How do I avoid the mistake?

I have the following function:

function [x,y,k] = Hord(fun,a,b,tolx,toly)

ya=feval(fun,a);
k=0;
while 1
    k=k+1;
    x=(a*fun(b)-b*fun(a))./(fun(b)-fun(a));
    y=feval(fun,x);
    if(x(k)-x(k-1)<=tolx)&(abs(y)<=toly), break, end
    if y*ya>0; a=x; ya=y;
    else b=x;
    end
end

Then my code is:

clc, clear all, close all, format short

x1=linspace(-pi/2,pi/2);%Заданий інтервал значень;
y1=cos(x1+0.3)-x1.^2;%Функція 1;
figure(1), plot(x1,y1,[-pi/2,pi/2], [0,0]),grid on, hold on%Графік;
f1=(@(x1) cos(x1+0.3)-x1.^2);%Анонімне задання функції 1;
format long
[X1,Y1] = Hord(f1, 0, pi/2, 1e-3, eps);%Перший додатний корінь;

X1,Y1%Виведення кореня;
plot(X1,Y1,'o','r--')%На графіку;

It should output the graph with a root, however, it only gives:

Array indices must be positive integers or logical values.

Error in Hord (line 9)

if(x(k)-x(k-1)<=tolx)&(abs(y)<=toly), break, end

Error in Lab7_var2 (line 36)

[X1,Y1] = Hord(f1, 0, pi/2, 1e-3, eps);%Перший додатний корінь;

How can I correct it?

Answer 1

[Torsten]

x in your code is a scalar, not a vector. Thus something like x(k) does not exist.

You could work with xold and x where xold would be the x-value of the previous iteration.

[Alisa-Oleksandra Kotliarova]

Thanks, that helped a lot!

Answer 2

[Image Analyst]

There is a thorough discussion in the FAQ: https://matlab.fandom.com/wiki/FAQ#%22Subscript_indices_must_either_be_real_positive_integers_or_logicals.%22

[Alisa-Oleksandra Kotliarova]

Thank you!