False position infinite loop

Hi there.

This function gets stuck in an infinite loop. Do you all have any suggestions for me?

    function [R, E] = myFalsePosition(f, xL, xR, tol)

        if sign (f(xL)) == sign(f(xR))
            error 'you are arrested!!!'
        end

        yL = f(xL);
        yR = f(xR);

        new_x = ((xR*yL) - (xL*yR))/(yL - yR);
        new_y = f(new_x);

        e = abs(new_y);
        E = e;

        while e > tol
            if f(xL)*f(new_x) > 0
                xL = new_x;
                yL = f(xL);

            else
                xR = new_x;
                yR = f(xR);
            end
        end

        new_x = ((xR*yL) - (xL*yR))/(yL - yR);
        new_y = f(new_x);
        R = [R new_x];
        e = abs(new_y);
        E = [E e];

    end

Answer 1

[Image Analyst]

Well you could tell us the values you used for f, xL, xR, tol when you called it. And you can use the debugger to figure out why "e" never falls below "tol". Using the debugger yourself will be your fastest course of action , rather than trying to debug it via back-and-forth Answers forum postings, which can take hours.

Answer 2

[per isakson]

I reformatted your function.

Neither e nor tol is changed in the while-loop. If &nbsp e > tol &nbsp is true when entering the loop it will remain true.

Possible, the end of the loop is not in the position, which you intended.

Answer 3

[My]

function p = myfalseposition(f,p0,p1,TOL,N0)

q0 = f(p0);
q1 = f(p1);

for i = 1:N0
    % False Position formülü
    p = p1 - q1*(p1-p0)/(q1-q0);
    
    if abs(p-p1) < TOL
        return
    end
    
    q = f(p);
    
    if q*q1 < 0
        p0 = p1;
        q0 = q1;
    end
    
    p1 = p;
    q1 = q;
end

disp('Method failed');
end


%Main
clear; clc;

f = @(x) cos(x) - x;

p0 = 0.5;
p1 = pi/2;
TOL = 1e-3;
N0 = 100;

p = myfalseposition(f,p0,p1,TOL,N0)