as a real-space formulation to a variety of quantum physical problems. Since the momentum space formulation, apart from a few exceptions , relies in most cases on a perturbative expansion, real-space methods offer non perturbative approaches and are therefore extremely important in applying RG ideas to strongly and complex correlated systems. It then turned out that for a variety of such physical models the real-space RG techniques give considerable bad results and the reason was unknown for nearly fifteen years. During that time some new real-space RG methods were discovered and some of them worked out very well whereas other methods failed without giving any insight to their failure. We like to refer the interested reader to the book of T.W. Burkhardt and J.M.J. van Leeuwen [@bl82] for a summary of work on this topic.\
Apart from these developments S.R. White and R.M. Noack published a series of papers containing a new idea for improving real-space RG techniques . Based on the understanding of the importance of boundary conditions for isolated blocks in real-space RG methods for quantum physical systems a numerical approach was invented to take sufficiently many boundary conditions into account during the RG procedure. Apart from the 