Abstract
We describe the essential mathematics that are to be invoked to arrive at a coherent description of energy conservation, propagation and reflection in discrete-space-discrete-time structures. These are the structures, which occur when hyperbolic equations are approximated numerically on a regular mesh in space-time. The combined use of discrete Fourier Transforms and energy measures produces a set of new and particularly elegant results relating to spurious reflection at computational boundaries. These results are sketched in this paper.