function J = JacDF(F,x0)
% Approximation of the Jacobian of the
% vectorial function F in x0 by means of 
% forward finite differences (DF)
% F is the function to be differentiated 
% (column vector)
% x0 evaluation point (column vector)
 delta = sqrt(eps); % passo per le DF
 n = length(x0); J = zeros(n,n); I = eye(n,n);
 for j = 1:n
   J(:,j) = (F(x0+delta*I(:,j))-F(x0))/delta;
  end
end