This thorn guide describes a fancy mechanism for registering gauge

conditions.  But at present, few (if any?) thorns seem to actually
use it.  So...  add a description of the way most (all?) gauge thorns
actually work at present, so the next innocent who comes along isn't
quite so confused as I was... :)


git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinBase/CoordGauge/trunk@57 edbb7e70-9571-45d5-a481-0a560a9b4751

1 files changed, 31 insertions, 3 deletions

diff --git a/doc/documentation.tex b/doc/documentation.tex
index 03005fc..2f4d458 100644
--- a/doc/documentation.tex
+++ b/doc/documentation.tex
@@ -17,11 +17,16 @@
 % Do not delete next line
 % START CACTUS THORNGUIDE
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 \begin{abstract}
-Base thorn to provide the infrastructure for dynamic gauge selection
+This thorn provides an infrastructure for dynamic gauge selection.
+However, at present (summer 2004) many thorns don't use this infrastructure.
 \end{abstract}
 
-\section{Purpose}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\section{The Infrastructure}
 
 The {\bf CoordGauge} implementation schedules five groups:
 
@@ -93,7 +98,30 @@ floating around.  It also allows us to keep the logic of the final
 selection in one place, thus allowing people to override this logic if
 they need to.
 
-\section{Comments}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\section{Current Status}
+
+As of summer 2004, many thorns don't use the above mechanism, instead
+they directly extend \\
+\verb|ADMBase::lapse_evolution_method| and/or
+\verb|ADMBase::shift_evolution_method|.  That is, the thorn implementing
+a coordinate condition thorn says in its \verb|param.ccl|:
+\begin{verbatim}
+EXTENDS KEYWORD lapse_evolution_method "Which lapse condition to use"
+{
+"super-duper" :: "my super-duper new lapse condition"
+} ""
+\end{verbatim}
+(and/or the equivalent for \verb|shift_evolution_method|).
+
+The thorn then schedules a routine in some suitable schedule bin/group
+(probably \verb|CCTK_PRESTEP| or \verb|MOL_PRESTEP|) to check
+\verb|ADMBase::lapse_evolution_method| and/or
+\verb|ADMBase::shift_evolution_method|, and if they're equal
+to the appropriate string, it does the coordinate condition.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
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 % END CACTUS THORNGUIDE