[ALPS-users] Full diagonalization for fixed N

Dear all, I perform a full diagonalization of Hubbard hamiltonian using a fulldiag application. I'm interested in energy spectrum for low densities of electrons only, or even fixed number of electrons on the lattice. So I don't really need to go over all subspaces with number of electrons N=0..N_total. I would be tankful for a hint where and how can I modify the code to fix the N? :) Best regards, Mykola