The numerical determination of apparent horizons

Abstract
The problem of determining apparent horizons in (3+1) numerical relativity is considered. The method proposed by Nakamura and co-workers (1984) is applied to initial data for several time-symmetric Schwarzschild black holes to determine the quantitative numerical properties of the algorithm. Several refinements are suggested to the method which lead to improved stability and convergence. Some circumstances in which it is not appropriate to use the method are found.