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% *======================================================================*
% Cactus Thorn template for ThornGuide documentation
% Author: Ian Kelley
% Date: Sun Jun 02, 2002
% $Header$
%
% Thorn documentation in the latex file doc/documentation.tex
% will be included in ThornGuides built with the Cactus make system.
% The scripts employed by the make system automatically include
% pages about variables, parameters and scheduling parsed from the
% relevant thorn CCL files.
%
% This template contains guidelines which help to assure that your
% documentation will be correctly added to ThornGuides. More
% information is available in the Cactus UsersGuide.
%
% Guidelines:
% - Do not change anything before the line
% % START CACTUS THORNGUIDE",
% except for filling in the title, author, date, etc. fields.
% - Each of these fields should only be on ONE line.
% - Author names should be separated with a \\ or a comma.
% - You can define your own macros, but they must appear after
% the START CACTUS THORNGUIDE line, and must not redefine standard
% latex commands.
% - To avoid name clashes with other thorns, 'labels', 'citations',
% 'references', and 'image' names should conform to the following
% convention:
% ARRANGEMENT_THORN_LABEL
% For example, an image wave.eps in the arrangement CactusWave and
% thorn WaveToyC should be renamed to CactusWave_WaveToyC_wave.eps
% - Graphics should only be included using the graphicx package.
% More specifically, with the "\includegraphics" command. Do
% not specify any graphic file extensions in your .tex file. This
% will allow us to create a PDF version of the ThornGuide
% via pdflatex.
% - References should be included with the latex "\bibitem" command.
% - Use \begin{abstract}...\end{abstract} instead of \abstract{...}
% - Do not use \appendix, instead include any appendices you need as
% standard sections.
% - For the benefit of our Perl scripts, and for future extensions,
% please use simple latex.
%
% *======================================================================*
%
% Example of including a graphic image:
% \begin{figure}[ht]
% \begin{center}
% \includegraphics[width=6cm]{MyArrangement_MyThorn_MyFigure}
% \end{center}
% \caption{Illustration of this and that}
% \label{MyArrangement_MyThorn_MyLabel}
% \end{figure}
%
% Example of using a label:
% \label{MyArrangement_MyThorn_MyLabel}
%
% Example of a citation:
% \cite{MyArrangement_MyThorn_Author99}
%
% Example of including a reference
% \bibitem{MyArrangement_MyThorn_Author99}
% {J. Author, {\em The Title of the Book, Journal, or periodical}, 1 (1999),
% 1--16. {\tt http://www.nowhere.com/}}
%
% *======================================================================*
% If you are using CVS use this line to give version information
% $Header$
\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{Yaakoub Y El Khamra \textless yye00@cct.lsu.edu\textgreater}
% The title of the document (not necessarily the name of the Thorn)
\title{}
% the date your document was last changed, if your document is in CVS,
% please use:
% \date{$ $Date$ $}
\date{May 26 2004}
\maketitle
% Do not delete next line
% START CACTUS THORNGUIDE
% Add all definitions used in this documentation here
% \def\mydef etc
% Add an abstract for this thorn's documentation
\begin{abstract}
Implement reduction operations using the new reduction API.
\end{abstract}
% The following sections are suggestive only.
% Remove them or add your own.
\section{Introduction}
A local reduction operation can be defined as an operation
on arrays (tuples) of variables resulting in a single number.
Typical reduction operations are sum, minimum/maximum value, and boolean
operations. A typical application is, for example,
finding the minimum value in an n-dimensional array.
This implementation of local reduction implements reduction and registers
functions using the new local reduction API as discussed on the developers
mailing lists.
\section{Physical System}
\section{Numerical Implementation}
The new local reduce thorn has several new features including index strides and offsets
for array indexing and full complex number support. Pending request, weight support
can be enabled (there are some issues that a mask is essentially a weight with 1 or 0 value).
Modifying or extending this thorn is quite a simple matter. The heart of all the reduction
operations is the large iterator macro in local_reductions.h. This iterator supports n-dimensional
arrays with offsets and strides. The iterator is used in all local reduction operators in this thorn.
To add a reduction operator, or change an existing one, all that needs to be done is to change the
actual reduction operation definition which is called from within the iterator to perform the reduction.
To use a custom local reduction operator from the new global reduction implementation, some values
must be returned to the global reduction implementation, such as the type of MPI reduction operation that
needs to be performed (MPI_SUM, MPI_MIN, MPI_MAX) and if the final result should include a division by the
total number of points used in the reduction. These are set in the parameter table with keys: mpi_operation and perform_division.
\section{Using This Thorn}
Please refer to the TestLocalReduce thorn in the CactusTest arrangement.
\subsection{Obtaining This Thorn}
\subsection{Basic Usage}
\subsection{Special Behaviour}
\subsection{Interaction With Other Thorns}
\subsection{Examples}
\subsection{Support and Feedback}
\section{History}
\subsection{Thorn Source Code}
\subsection{Thorn Documentation}
\subsection{Acknowledgements}
\begin{thebibliography}{9}
\end{thebibliography}
% Do not delete next line
% END CACTUS THORNGUIDE
\end{document}
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