Help with Newton's method function?

This is the function I've been making to run Newton's method, but I can't get it to work. Any help with what I might be missing? Thanks!

function xn = newtonmethod(f,fd,x0,tol)    
xn=x0;    
err=abs(f(xn)-0);   
i=0;
while err>tol
    i=i+1;
    xnew=xn-(f(xn)/fd(xn));
    err=abs(f(xnew)-0);
end

Answer 1

[Walter Roberson]

I suspect your

      err=abs(f(xnew)-0);

should be

      err=abs(f(xnew)-f(xn));

unless you know that your f() has a "right" value of 0.

[Lauren Hux]

It does. Do you see anything else wrong with the code?

[Walter Roberson]

You do not update xn = xnew