I've been meaning to learn how to use DMRG (density matrix renormalization group) for a long time. Which package has the easiest learning curve? I specifically mean it should be easy to actually learn how to write your own calculations that do nontrivial things, not just run an example code that they provide.
Edit: I want to do calculations on spin systems or lattice bosons/fermions. Heisenberg or Hubbard-like models.