A critical function K( nu ) of a two degrees of freedom Hamiltonian system represents a fractal boundary between regular and chaotic motion as a function of frequency. The method of modular smoothing uses the transformation properties of K( nu ) for unit translation and inversion of nu to provide a rapid method of computing K( nu ). The authors demonstrate two unusual properties of the method: it is simpler for continuous time systems than for maps, and for at least one system exact results can be obtained.