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Diffstat (limited to 'doc/documentation.tex')
| -rw-r--r-- | doc/documentation.tex | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/doc/documentation.tex b/doc/documentation.tex index d06fcd2..5cb2fff 100644 --- a/doc/documentation.tex +++ b/doc/documentation.tex @@ -173,8 +173,10 @@ takes the absolute value of $\eta$ before interpolating. The 2-D grid covers the region $|\eta| \in [0,\texttt{etamax}]$, $\theta \in [0,\pi]$, where the parameter \verb|etamax| defaults to 5. If any 3-D grid point's $(|\eta|,\theta)$ is outside this 2-D grid, -this thorn will abort with a fatal error message from the interpolator, -typically looking like this: +this thorn will abort with a fatal error message from the interpolator. +In practice, the most common cause of such an out-of-range point is +the 3-D grid having a grid point at, or very near to, the origin. +For example: \begin{verbatim} WARNING level 1 in thorn AEILocalInterp processor 0 host ic0087 (line 1007 of /nfs/nethome/pollney/runs/CactusDev/arrangements/AEIThorns/AEILocalInterp/src @@ -193,11 +195,11 @@ WARNING level 0 in thorn IDAxiBrillBH processor 0 host ic0087 -> error in interpolator: ierror= -1002 \end{verbatim} -What happened here is that the 3-D grid had a point right at the origin +Here the 3-D grid had a point right at the origin (which by virtue of~\eqref{IDAxiBrillBH/eta-coord} would have given $\eta = -\infty$), but some software moved the grid point by $10^{-16}m$ -or so to avoid divisions by zero, giving -$\eta \equiv \ln (2 \,{\times}\, 10^{-16}) \approx -36$. +or so (the standard Cactus work-around to try to avoid divisions by zero), +giving $\eta \equiv \ln (2 \,{\times}\, 10^{-16}) \approx -36$. The absolute value of this is the ``$x$'' coordinate the interpolator is complaining about. |