Finding Apparent Horizons in Dynamic 3D Numerical Spacetimes
  We have developed a general method for finding apparent horizons in 3D numerical relativity. Instead of solving for the partial differential equation describing the location of the apparent horizons, we expand the closed 2D surfaces in terms of symmetric trace--free tensors and solve for the expansion coefficients using a minimization procedure. Our method is applied to a number of different spacetimes, including numerically constructed spacetimes containing highly distorted axisymmetric black holes in spherical coordinates, and 3D rotating, and colliding black holes in Cartesian coordinates. 
P. Anninos, K. Camarda, J. Libson, J. Mass\'o, E. Seidel, W.-M. Suen