A proposal of a Renormalization Group transformation
  We propose a family of renormalization group transformations characterized by free parameters that may be tuned in order to reduce the truncation effects. As a check we test them in the three dimensional XY model. The Schwinger--Dyson equations are used to study the renormalization group flow. 
L.A. Fernandez, A. Munoz Sudupe, J.J. Ruiz-Lorenzo and A. Tarancon