Test-beds and applications for apparent horizon finders in numerical relativity

We present a series of test-beds for numerical codes designed to find appar ent horizons. We compare three apparent horizon finders that use different numerical methods: one of them in axisymmetry and two which are fully three dimensional. We concentrate first on a toy model that has a simple horizon structure, and then go on to study single and multiple black hole datasets . We use our finders to look for apparent horizons in Brill wave initial da ta where we discover that some results published previously are not correct . For pure wave and multiple black hole spacetimes, we apply our finders to survey parameter space.