The Perfect Laplace Operator for Non-Trivial Boundaries
  The application of Renormalization Group (RG) methods to find perfect discretizations of partial differential equations is a promising but little investigated approach. We calculate the classically perfect fixed-point Laplace operator for boundaries of non-trivial shape analytically and numerically and present a parametrization that can be used for solving the Poisson equation. 
S. Hauswirth