Error in code: attempted to access x(0)

I am writing a code for fixed point iteration. Whenever I try to run the code, I get an error that says:

Attempted to access x(0); index must be a positive integer or logical.

It says the error is with x(0)=10000000.

This is my code:

g(x) = (1/2)*cos(x);
p = input('What is the initial guess \n');
x(0)=10000000
tol = input('What is the relative error tolerance \n');
imax = input('What is the iteration limit \n');
i = 0

while abs(x(1)-x(0)) <= (x(1)*tol) && i > imax
    x(0) = x(1)
    x(1) = (1/2)*cos(x(0))
    i = i+1
end

fprintf('x1 is %g \n',x(1))

Answer 1

[Blair Ebeling]

The code showed up weird, this is the code:

 g(x) = (1/2)*cos(x);
 p = input('What is the initial guess \n');
 x(0)=10000000
 tol = input('What is the relative error tolerance \n');
 imax = input('What is the iteration limit \n');
 i = 0

 while abs(x(1)-x(0)) <= (x(1)*tol) && i > imax   
    x(0) = x(1)
    x(1) = (1/2)*cos(x(0))
    i = i+1
 end

 fprintf('x1 is %g \n',x(1))

Answer 2

[Walter Roberson]

MATLAB has never supported indexing at 0. x(0) has always been an error in MATLAB. The first element of array or vector x is x(1)

In other words, add 1 to all of your subscript references. x(0+1), x(1+1)

There is no point in using a vector in the code your show: you might as well use variables named x0 and x1 . A vector would be useful if you were referring to x(i) .

Note by the way that your code refers to x(1) before having assigned anything to x(1)