Calculation of effective Hamiltonians for renormalized or non-Hamiltonian systems

We develop a method for calculating renormalized Hamiltonians based on the Brandt-Ron representation of renormalization-group transformations. Our approach allows us to make a stable calculation for larger sets of renormalized coupling constants than either the Swendsen or the Gupta-Cordery methods, thus reducing the effects of truncation in renormalization-group calculations. The generality of the Brandt-Ron representation also makes it suitable for analyzing a broader class of models including driven diffusive systems. Another advantage of our approach is that it contains internal criteria that provide information on the error involved in truncation approximations.