function fprime=c_8_p_4_fn_prime(x)
% The derivative (gradient) of the function we want to minimize
fprime = zeros(2,1);
fprime(1) = 400 * ( x(1)^2 - x(2) ) * x(1) - 2 * (1 - x(1));
fprime(2) = -200 * ( x(1)^2 - x(2) );