[ALPS-users] Fwd: Setting Constraint

Dear ALPS Member, I am trying to run ALPS DMRG to calculate gap for a spin system on 3-chain lattice. My energy eigenvalue is degenerate and I am trying to divide the system to different sector using the constraint. I want to set an eigenvalue of one operator to have a specific value. My problem is the operator which divide my Hilbert space to different sector is not local and depends on several site. I am wondering if I can do that with constraint. Should I define a new quantum number other than Sz? Thank you for your help, Best, Ali