Hi,

Thanks for the answer about the truncation error. I felt kind of dumb that I hadn't thought of that before, but I don't use unix all that often. I just read through Steven White's 2005 paper "Density matrix renormalization group algorithms with a single center site." I was looking through the dmrg code trying to figure out how to implement the single site method. I was wondering what the general consensus is about this method before I continue trying to implement it. Here is my goal: I would like to try to find the Haldane gap in S=1 Heisenberg ladders. I know that the accepted method for doing this in 1D is to make the ends of the chain be S=1/2 to avoid the end effects. Will this work in ladders as well? I was thinking that the single site method would just allow me to use periodic boundary conditions and avoid the end site problems. I also don't know how to put S=1/2 sites at the ends of the lattice in ALPS. Does anyone know how to do this? Can I just set local_S for each site of the lattice?

Thanks, Justin