bananaobj(x)

function [F,J] = bananaobj(x)
% Evaluate the vector function and the Jacobian matrix for 
% the system of nonlinear equations derived from the general 
% n-dimensional Rosenbrock function.
% Get the problem size
n = length(x);  
if n == 0, error('Input vector, x, is empty.'); end
if mod(n,2) ~= 0, 
   error('Input vector, x, must have an even number of components.'); 
end
% Evaluate the vector function
odds  = 1:2:n;
evens = 2:2:n;
F=x(:);
% F = zeros(n,1);
F(odds,1)  = 1-x(odds);
F(evens,1) = 10.*(x(evens)-x(odds).^2); 
% Evaluate the Jacobian matrix if nargout > 1
if nargout > 1
   c = -ones(n/2,1);    C = sparse(odds,odds,c,n,n);
   d = 10*ones(n/2,1);  D = sparse(evens,evens,d,n,n);
   e = -20.*x(odds);    E = sparse(evens,odds,e,n,n);
   J = C + D + E;
end