Matlab - simple newton's method ex

function r = doNewton(f,x0,x,err)
 
 while abs(x0 - x) > err
  
  x0, (x0 - x)

  x0 = x0 - (polyval(f,x0))/polyval(polyder(f),x0);

  
 end
 
 

 r = x0;
end