From e18c71e353756e2d9782fc0f8c4dd38dad999d3e Mon Sep 17 00:00:00 2001 From: jthorn Date: Mon, 13 Jun 2005 15:36:30 +0000 Subject: += explanation that you must use a staggered grid git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinInitialData/IDAxiBrillBH/trunk@75 0a4070d5-58f5-498f-b6c0-2693e757fa0f --- doc/documentation.tex | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/doc/documentation.tex b/doc/documentation.tex index 781430b..cfd981b 100644 --- a/doc/documentation.tex +++ b/doc/documentation.tex @@ -149,7 +149,14 @@ and outer boundary condition, a Robin condition: This thorn solves equation~(\ref{IDAxiBrillBH/eqn:ham-linear}) on a 2-D $(\eta,\theta)$ grid. However, Cactus needs a 3-D grid, typically with Cartesian coordinates. Therefore, this thorn interpolates $\psi$ and its -$(\eta,\theta)$ derivatives to the Cartesian grid. +$(\eta,\theta)$ derivatives to the Cartesian grid. More precisely, for +each Cactus grid point, this thorn calculates the corresponding $(\eta,\theta)$ +coordinates, and interpolates the 2-D solution to that point. + +[Note that since $\eta$ (defined by~$(\ref{IDAxiBrillBH/eta-coord})$) +is a \emph{logarithmic} radial coordinate, this thorn will fail if +there's a Cartesian grid point at the origin. Use a staggered grid +to work around this problem.] The parameters \verb|neta| and \verb|nq| specify the resolution of this thorn's 2-D grid in $\eta$ and $\theta$ respectively.%%% -- cgit v1.2.3