MATLAB: Newton method to find polinom roots

newton

Hi!
I wrote Newton method in matlab to find the polinom roots but I didn't get it which the answer write.
p = [ 1 -1 -6 0]
x0 = 2;
So this is my code:
function [pd,X] = newtonMethod(p,x0)
n = length(p); 
pd = polyder(p) 
result = [];
for i = 1:8
    fx(i) = polyval(p,x0);
    fdx(i) = polyval(pd,x0); 
    x(i) = x0 - (fx/fdx);
    result = [result; x(i)];
    x0 = x(i); 
end
result
end
And i get this:
6.0000
4.4028
2.9345
1.4956
0.0557
-1.3792
-2.8141
-4.1472
But the answer:
6.0000
4.4000
3.4891
3.0912
3.0041
3.0000
3.0000
3.0000

Best Answer

  p = [ 1 -1 -6 0]
  x0 = 2;
  n = length(p); 
  pd = polyder(p) 
  result = [];
  for i = 1:8
    fx = polyval(p,x0);
    fdx = polyval(pd,x0); 
    x0 = x0 - (fx/fdx);
    result = [result; x0]; 
  end
  result
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