A Proposal of a Renormalization Group Transformation for Lattice Field   Theories
  We propose a new Real Space Renormalization Group transformation useful for Monte Carlo calculations in theories with global or local symmetries. From relaxation arguments we define the block-spin transformation with two tunable free parameters, adapted to the system's action. Varying them it is possible to place the fixed point very close to the simulation point. We show how the method works in a simple model with global symmetry: the three dimensional XY model. 
L.A.Fernandez, Munoz Sudupe, J.J.Ruiz-Lorenzo and A.Tarancon