Apparent horizons in simplicial Brill wave initial data
  We construct initial data for a particular class of Brill wave metrics using Regge calculus, and compare the results to a corresponding continuum solution, finding excellent agreement. We then search for trapped surfaces in both sets of initial data, and provide an independent verification of the existence of an apparent horizon once a critical gravitational wave amplitude is passed. Our estimate of this critical value, using both the Regge and continuum solutions, supports other recent findings. 
Adrian P. Gentle, Daniel E. Holz, Warner A. Miller and John A. Wheeler