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% If you are using CVS use this line to give version information

\documentclass{article}

% Use the Cactus ThornGuide style file
% (Automatically used from Cactus distribution, if you have a
%  thorn without the Cactus Flesh download this from the Cactus
%  homepage at www.cactuscode.org)
\usepackage{../../../../doc/latex/cactus}

\begin{document}

% The author of the documentation
\author{Erik Schnetter \textless schnetter@cct.lsu.edu\textgreater}

% The title of the document (not necessarily the name of the Thorn)
\title{InterpToArray}

\date{June 30, 2010}

\maketitle

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% START CACTUS THORNGUIDE

% Add all definitions used in this documentation here
%   \def\mydef etc

% Add an abstract for this thorn's documentation
\begin{abstract}
  Interpolate grid functions to grid arrays on a regular grid of
  locations, so that these can e.g.\ be output more easily.
\end{abstract}

% The following sections are suggestive only.
% Remove them or add your own.

\section{Introduction}
Some post-processing and visualisation tools cannot handle mesh
refinement or multi-block systems.  These tools then require
interpolating the result onto a regular, uniform grid.  This is what
this thorn does.

InterpToArray can interpolate to 0D, 1D, 2D, and 3D grids.  The
interpolation result is stored in grid arrays.  These can be either
replicated or distributed over all processes.  Note that using
replicated (DISTRIB=constant) grid arrays can require a substantial
amount of memory on each process.

\section{Numerical Implementation}
InterpToArray uses standard Cactus interpolators such as PUGHInterp or
CarpetInterp.

\section{Using This Thorn}
The variables which should be interpolated are specified by
parameters; currently, up to 100 variables can be interpolated.

The interpolator and its options are also specified via parameters.

Finally, the locations of the points of the regular grid are also
specified via parameters.  These grid points are specified via an
\emph{origin} and \emph{offsets}, and they do not have to be aligned
with the coordinate axes.  For example, a 2D grid is specified via
three (real) vectors $x^a$, $di^a$, and $dj^a$, and via its (integer)
size $ni$ and $nj$.  The coordinates of the grid points are then given
via
$$
x^a(i,j) = x^a + i \cdot di^a + j \cdot dj^a
$$
for $0 \le i < ni$ and $0 \le j < nj$.  Grids with other dimensions
are specified equivalently.

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\end{document}