  The Schrodinger equation with a two-dimensional delta-function potential is a
simple example of an asymptotically free theory that undergoes dimensional
transmutation. Renormalization requires the introduction of a mass scale, which
can be lowered perturbatively until an infrared cutoff produced by
non-perturbative effects such as bound state formation is encountered. We
outline the effective field theory and similarity renormalization group
techniques for producing renormalized cutoff hamiltonians, and illustrate the
control of logarithmic and inverse-power-law errors both techniques provide.
