How do I stop the infinite loop in this fixed point iteration code?

Here is my code:

      %fixedpoint
  g=@(x) 1-(1/7).*exp(1).^x;
  n=1;
  x(1)=0.5;
  x(2)=g(x(1));
  tol = (0.5*10e-10);
  error = abs((x(n+1))-(x(n)));

while error>tol
    n=n+1;
    x(n+1)=g(x(n));
end
format long
disp(x(n))
disp(n)
semilogy()

I cannot figure out how to stop the infinite loop I've tried cVals, and allowing for the max iterations (which I could have been wrong in the code I put in). Also, Im not sure what goes in semilogy() to plot the error as a function of n on the same set of axes. Any help would be greatly appreciated, thank you.

[Sarah Harvey]

Also, it didn't do the infinite loop when I did not have error=abs(((x(n+1))-(x(n))) before the loop, and just, abs(((x(n+1))-(x(n)))>tol as the while loop.

Answer 1

[Walter Roberson]

Your code has

while error>tol
  n=n+1;
  x(n+1)=g(x(n));
end

You do not change the variable "error" inside the loop, so if the loop is ever entered at all, there is no way out of the loop. You need to change "error" inside the loop.

Note: it is not a good idea to use "error" as the name of a variable, as that interferes with the use of the important MATLAB routine named "error"

[Sarah Harvey]

Thank you so much! Also, do you know about the semilogy problem?

[Walter Roberson]

You would record the error at each step and semilogy() that.