function f = RosenbrockDF(X)
% Gradient of the Rosenbrock's function (2D)
% X is a 2D vector.
% K. Ming Leung, 09/29/03

X1 = X(1); X2 = X(2);
f = [(400*X1.*X1+2-400*X2).*X1-2; -200*(X1.^2-X2)];

