Cactus Code Thorn EHFinder
Authors    : Peter Diener
CVS info   : $Header$
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Purpose of the thorn:

To find the event horizon of a numerical spacetime by integrating a null
surface backwards in time. The basic equation is equation 2 in Anninos et. al,
Physical Review Letters, 74, 630, 1995.

The surface will be parametrized as the 0 value isosurface of a level
set function. Hopefully this will work when the topology changes from
one common event horizon to two individual event horizons.