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\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/ThornGuide/cactus}
\begin{document}
\title{PUGHReduce}
\author{Gabrielle Allen, Thomas Radke}
\date{$ $Date$ $}
\maketitle
% Do not delete next line
% START CACTUS THORNGUIDE
\begin{abstract}
Reductions operations which are performed using the PUGH driver
\end{abstract}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Purpose}
%
This thorn registers a number of reduction operators with the flesh. The
reductions are performed using internals of the PUGH driver, so that this
thorn can only be used when {\tt CactusPUGH/PUGH} is active.\\
The reduction operations this thorn registers are\\
\begin{tabular}{|l|l|l|}
\hline
Reduction Operator & Calculates & By \\
\hline
{\tt average$^*$} & the average of a grid variable & $ \sum{ GV }/n $ \\
{\tt minimum$^*$} & the minimum of a grid variable & $ \min{ GV } $ \\
{\tt maximum$^*$} & the maximum of a grid variable & $ \max{ GV } $ \\
{\tt sum$^*$} & the sum of the elements of a grid variable & $ \sum{ GV } $ \\
{\tt norm1} & the L1 norm of a grid variable & $ \left(\Sigma | GV | \right)/n $ \\
{\tt norm2} & the L2 norm of a grid variable & $ \sqrt{(\Sigma GV^2)/n} $ \\
{\tt norm\_inf} & the Inf norm of a grid variable & $ \max{| GV |} $ \\
\hline
\end{tabular}\\
In the formulas $GV$ is the grid variable to be reduced, and $n$ denotes the
number of its elements. Reduction operators marked with $^*$ cannot be applied
to grid variables of complex datatype.
%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Examples}
%
The following C example illustrates how the get the maximum value of a grid
function.
%
\begin{verbatim}
int vindex; /* grid variable index */
CCTK_REAL result; /* resulting reduction value */
int target_proc; /* processor to hold the result */
int reduction_handle; /* handle for reduction operator */
char *reduction_name; /* reduction operator to use */
/* want to get the maximum for the wavetoy grid function */
reduction_name = "maximum";
vindex = CCTK_VarIndex ("wavetoy::phi");
/* the reduction result will be obtained by processor 0 only */
target_proc = 0;
/* get the handle for the given reduction operator */
reduction_handle = CCTK_ReductionHandle (reduction_name);
if (reduction_handle >= 0)
{
/* now do the reduction using the flesh's generic reduction API
(passing in one input, expecting one output value of REAL type) */
if (CCTK_Reduce (cctkGH, target_proc, reduction_handle,
1, CCTK_VARIABLE_REAL, &result, 1, vindex) == 0)
{
if (CCTK_MyProc (cctkGH) == target_proc)
{
printf ("%s reduction value is %f\n", reduction_name, result);
}
}
else
{
CCTK_VWarn (1, __LINE__, __FILE__, CCTK_THORNSTRING,
"%s reduction failed", reduction_name);
}
}
else
{
CCTK_VWarn (1, __LINE__, __FILE__, CCTK_THORNSTRING,
"Invalid reduction operator '%s'", reduction_name);
}
\end{verbatim}
% Do not delete next line
% END CACTUS THORNGUIDE
\end{document}
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