Trying to make loop break when Xnew=Xlast, but the program stops at the wrong numbers.

Hey I'm trying to make a loop that keeps going till Xnew=Xlast, but the numbers aren't coming out right. I know my formulas are correct, but something is still messing up.

If I input r0=120, r1=60, r2=140, r3=80, theta0=pi, theta1=pi/3, theta2=1, and theta3=3 I should get the numbers 0.077 and 4.044, but for some reason I'm getting 0.0005 and 5.0754. I'm pretty sure it's a code error. I'll put my code below. Can anyone help?

function [ theta2, theta3 ] = kenimaticprob( r0, r1, r2, r3, theta0, theta1 )
%UNTITLED2 Summary of this function goes here
%   Detailed explanation goes here
r0=input('enter the length of fixed link r0: ')
r1=input('enter the length of the link r1: ')
r2=input('enter the length of coupler link r2: ')
r3=input('enter the length of driven crank link r3: ')
theta0=input('enter the value of the angle between the fixed link and the horizontal theta0: ')
theta1=input('enter the value of the angle between the crank link and the fixed link theta1: ')
theta2=input('guess the angle theta2: ')
theta3=input('guess the angle theta3: ')

f1=r2*cos(theta2)+r3*cos(theta3)+r0*cos(theta0)+r1*cos(theta1);
f2=r2*sin(theta2)+r3*sin(theta3)+r0*sin(theta0)+r1*sin(theta1);
f=[f1; f2];
g=[-r2*sin(theta2), -r3*sin(theta3) ; r2*cos(theta2), r3*cos(theta3)];
Xnew=[theta2; theta3]-inv(g)*f;
Xlast=[theta2; theta3];
Xnew=Xlast-inv(g)*f;
loop=1
Xnew=Xlast-inv(g)*f;
disp(Xnew)
Xlast=Xnew; 
while(1)
f1=r2*cos(Xnew(1))+r3*cos(Xnew(2))+r0*cos(theta0)+r1*cos(theta1);
f2=r2*sin(Xnew(1))+r3*sin(Xnew(2))+r0*sin(theta0)+r1*sin(theta1);
f=[f1; f2];
G=[-r2*sin(Xnew(1)), -r3*sin(Xnew(2));r2*cos(Xnew(1)), r3*cos(Xnew(2))];
inv(G);

loop=loop+1

Xnew=Xlast-inv(g)*f;
disp(Xnew)
error_1=(Xnew(1)-Xlast(1))/Xnew(1);
error_2=(Xnew(2)-Xlast(2))/Xnew(2);
error_max=max(error_1,error_2);

es=1*10^(-4);

if(error_max>es)
    Xlast=Xnew;
else
    Xnew;
    break
end
end

Answer 1

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

[Image Analyst]

He isn't comparing for equality, despite what his subject line says, his code is checking if they're within a tolerance (a ratio of 1e-4). I wonder if either his "true" values aren't really the true values, or if his equations are wrong. By the way, he should be checking error_max=max(abs(error_1),abs(error_2)); just in case the error(s) might ever be negative.