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Diffstat (limited to 'doc/documentation.tex')
| -rw-r--r-- | doc/documentation.tex | 9 |
1 files changed, 8 insertions, 1 deletions
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.%%% |