function [f,g,H] = rosen(x,Hessflag)

% ROSENBROCK 
%
% INPUTS:
% X      - a 2-D vestor
% PARAMS - Not used, but included for compatibility with LINESEARCH   
%
% OUTPUT:
% F      - a scalar, the Rosenbrock evaluated at X
% G      - a 2x1 vector, the Gradient of the Rosenbrock evaluated at X
%
% This function evaluates the Rosenbrock function:
%      f: R^2        ---> R
%         x=[x1; x2] |---> 100(x2-x1^2)^2 + (1-x1)^2
%
% as well as its gradient:
%      g: R^2        ---> R^2
%         g=[x1; x2] |---> [-400*x1*(x2-x1^2) - 2(1-x1); 200(x2-x1^2)]
%
% And finally, also the hessian of f.
%
%      H = [-400*(x2-3*x1^2) + 2, 400*x1;
%            -400*x1,             200]


f=100*(x(2)-x(1).^2).^2 + (1-x(1)).^2;

g=[-400*x(1).*(x(2)-x(1).^2)-2*(1-x(1)); 200*(x(2)-x(1).^2)];

H=[-400*(x(2)-3*x(1)^2)+2, -400*x(1); -400*x(1), 200];