document the new

   min_horizon_radius_points_for_maks
parameter


git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinAnalysis/AHFinderDirect/trunk@1211 f88db872-0e4f-0410-b76b-b9085cfa78c5

1 files changed, 29 insertions, 0 deletions

diff --git a/doc/documentation.tex b/doc/documentation.tex
index 46a8ec8..20a3907 100644
--- a/doc/documentation.tex
+++ b/doc/documentation.tex
@@ -1019,6 +1019,35 @@ and $z$ Cactus grid spacings)%%%
 		   else \>$\verb|mask| \assign \verb|outside_value|$	\-%%%\\
 		\end{tabbing}
 	\end{description}
+
+\item[\code{min\_horizon\_radius\_points\_for\_mask}]
+\mbox{}\\
+	By default, \thorn{AHFinderDirect} sets the mask for each
+	apparent horizon found.  If we're using mesh refinement, it's
+	possible for an apparent horizon to be found on a coarse grid,
+	and the masked region to be only a few grid points across on
+	a fine grid.  This causes some other Cactus thorns
+	(\eg{} \thorn{LegoExcision}) to crash. :(
+
+	This parameter can be used to avoid this problem:
+	\thorn{AHFinderDirect} only sets the mask for an
+	apparent horizon if
+	\begin{equation}
+	r_{\min} \ge \verb|min_horizon_radius_points_for_mask| * \Delta x
+	\end{equation}
+	where $r_{\min}$ is the minimum coordinate radius of
+	the apparent horizon (about the local coordinate origin),%%%
+\footnote{%%%
+	 This may change soon to $r_\text{inner}$
+	 or $r_\text{outer}$.
+	 }%%%
+{}	and $\Delta x$ is the maximum of the Cactus $x$, $y$, and $z$
+	grid spacings on the current Cactus grid.  If this condition
+	isn't satisfied, then \thorn{AHFinderDirect} skips setting the
+	mask for this apparent horizon, just as if this apparent
+	horizon wasn't found.  (Note that the various output files
+	are still written as usual; it's only the mask processing
+	for this horizon that's skipped.)
 \end{description}
 
 \thorn{AHFinderDirect} supports two types of mask grid functions;