Added note that the "derivatives" are actually the derivatives divided by the

conformal factor.

Added some more notes on the use of the metric_type parameter and conformal_state
variable to try to alleviate some confusion on their use.

Tom


git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinBase/StaticConformal/trunk@6 0cbbb82d-14ec-4423-a1fb-2ab18257ecaa

1 files changed, 23 insertions, 0 deletions

diff --git a/doc/documentation.tex b/doc/documentation.tex
index 519a092..0f80e0d 100644
--- a/doc/documentation.tex
+++ b/doc/documentation.tex
@@ -28,6 +28,16 @@ derivatives {\bf psixx}, {\bf psixy}, {\bf psixz}, {\bf psiyy}, {\bf
 psiyz}, and {\bf psizz} depending on the setting of the {\bf
 conformal\_storage} parameter.
 
+Note that the first and second ``derivative'' grid functions have an
+additional factor of $1 / \psi$ normalisation since this is the most
+common use of the derivative.  I.e. the grid functions are
+
+$$ \psi $$
+$$ \psi_i/\psi$$
+and
+
+$$ \psi_{ij}/\psi $$
+
 Thorns need to check the value of the grid scalar 
 {\bf conformal\_state} to determine how many levels of these variables have
 actually been calculated.
@@ -49,6 +59,19 @@ The conformal factor and its first and second derivatives have been calculated.
 The {\bf StaticConformal} thorn itself does not calculate any conformal
 factor, but does initialise the {\bf conformal\_state} variable to 0. 
 
+Please note, no thorn should use the conformal\_state variable unless
+metric\_type is "static conformal".  The conformal\_state variable is
+not assigned storage or initialised by the StaticConformal thorn in
+any other case.
+
+However thorns are free to themselves assigned storage for
+conformal\_state and initialised it to zero if metric\_type is
+"physical".  In this one case is it safe for them to use
+the conformal\_state variable if metric\_type is not "static
+conformal".  This method allows them to use just one set of ifs rather
+than first checking the metric\_type and then the conformal\_state
+variable if the metric\_type is "static conformal".
+
 % Automatically created from the ccl files by using gmake thorndoc
 \include{interface}
 \include{param}