I am needing to implement Steffenson's method. Need help debugging my code, including help with suggestions on avoiding unnecessary function evaluations

format long

n = 100;

tol = 10^(-15);

g = @(x) -erf(2*(x - 1));

x(1) = 0;

i = 1;

while i <= n

i = i + 1;

x(i) = x(i) - (((g(x(i)) - x(i))^2)/(g(g(x(i))) - 2*g(x(i)) + x(i)));

if abs(x(i)-x(i-1)) <= tol*abs(x(i))

break

end

end