Newton's Method error message

I keep recieving this error code and I don't know how to fix it or if it will even work after i fix it. The initial value is supposed to be 20 and the threshold is 0.1.

Index exceeds the number of array elements (0).

Error in EE291_Pr01_crise_kylee_part2 (line 17)

w(n+1)= w(n)-(z(w(n))/dz(x(n)));

clc;
clear;
z=@(w) (100+(0.5*w/(.0000003*w^2+1))); 
c=0.0000003;
a=50000000;
b=10000000;
dz=@(w) (a*(3*w^2-b))/((3*w^2+b)^2);
w0=20;
w(1)=w0;
thr=0.1; 
err=1;
n=0;
w=zeros(0, 10000000);
while err>=1e-1
%set while-conditions 
n=n+1;
w(n+1)= w(n)-(z(w(n))/dz(x(n))); 
%compute next iterate 
err=abs((w(n+1)-w(n))/w(n+1))*100;                              
%compute error 
end
disp(n);
disp(w);
disp(err);

Answer 1

[Jim Riggs]

The variable x is not defined in

w(n+1) = w(n) - (z(w(n))/dz(x(n)));