NEWTON MATLAB

h=0.01;
f= @(x) x.^3+x.^2-20*x;
df= @(x) (f(x+h)-f(x))/h;
ddf= @(x) (f(x+2*h)-2*f(x+h)+f(x))/(h^2);
x = 6;
a = 0;
b = 6;
k = 0;
while ( df(x) > 0.001 )
    x1=x-(df(x)/ddf(x));
    k=k+1;
    x=x1;
end
wynik_newton = x
n_newton = k