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

We present a series of test-beds for numerical codes designed to find apparent 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 data 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.