3.3 Using multiple event/apparent horizon finders
It is useful to have multiple event or apparent horizon finders available: Their strengths
and weaknesses may complement each other, and the extent of agreement or disagreement
between their results can help to estimate the numerical accuracy. For example, Figure 11
shows a comparison between the irreducible masses of apparent horizons in a binary black
hole coalescence simulation (Alcubierre et al. [5
, Figure 4b]), as computed by two different
apparent horizon finders in the
Cactus toolkit, AHFinder and AHFinderDirect. In this
case the two agree to within about 2% for the individual horizons and 0.5% for the common
horizon.