3 Prototype Characteristic Evolution Codes
Limited computer power, as well as the instabilities arising from non-hyperbolic formulations of
Einstein’s equations, necessitated that the early code development in general relativity be restricted to
spacetimes with symmetry. Characteristic codes were first developed for spacetimes with spherical
symmetry. The techniques for relativistic fields which propagate on null characteristics are similar to the
gravitational case. Such fields are included in this section. We postpone treatment of relativistic fluids,
whose characteristics are timelike, until Section 5.