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\subsection{Introduction} |
\subsection{Introduction} |
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The \texttt{exch2} package is an extension to the original cubed |
The \texttt{exch2} package is an extension to the original cubed |
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sphere exchanges to allow more flexible domain decomposition and |
sphere topological configuration that allows more flexible domain |
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parallelization. Cube faces (subdomains) may be divided into whatever |
decomposition and parallelization. Cube faces (also called |
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number of tiles that divide evenly into the grid point dimensions of |
subdomains) may be divided into any number of tiles that divide evenly |
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the subdomain. Furthermore, the individual tiles may be run on |
into the grid point dimensions of the subdomain. Furthermore, the |
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separate processors in different combinations, and whether exchanges |
individual tiles may be run on separate processors in different |
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between particular tiles occur between different processors is |
combinations, and whether exchanges between particular tiles occur |
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determined at runtime. |
between different processors is determined at runtime. This |
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flexibility provides for manual load balancing across a relatively |
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arbitrary number of processors. |
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The exchange parameters are declared in |
The exchange parameters are declared in |
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\filelink{pkg/exch2/W2\_EXCH2\_TOPOLOGY.h}{pkg-exch2-W2_EXCH2_TOPOLOGY.h} |
\filelink{pkg/exch2/W2\_EXCH2\_TOPOLOGY.h}{pkg-exch2-W2_EXCH2_TOPOLOGY.h} |
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and assigned in |
and assigned in |
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\filelink{pkg/exch2/w2\_e2setup.F}{pkg-exch2-w2_e2setup.F}, both in |
\filelink{pkg/exch2/w2\_e2setup.F}{pkg-exch2-w2_e2setup.F}. The |
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the \texttt{pkg/exch2} directory. The validity of the cube topology |
validity of the cube topology depends on the \texttt{SIZE.h} file as |
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depends on the \texttt{SIZE.h} file as detailed below. Both files are |
detailed below. Both files are generated by Matlab scripts in ?? |
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generated by Matlab scripts and should not be edited. The default |
check these in already! and should not be edited. The default files |
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files provided in the release set up a cube sphere arrangement of six |
provided in the release configure a cubed sphere arrangement of six |
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tiles, one per subdomain, each with 32x32 grid points, running on a |
tiles, one per subdomain, each with 32$\times$32 grid points, all |
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single processor. |
running on a single processor. Pregenerated examples of these files |
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with alternate topologies are provided in ??. |
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\subsection{Invoking exch2} |
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To use exch2 with the cubed sphere, the following conditions must be met: |
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- the exch2 package is included when \texttt{genmake2} is run. The |
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easiest way to do this is to add the line \texttt{exch2} to the |
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\texttt{profile.conf} file -- see Section \ref{sect:buildingCode} |
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for general details. \\ |
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- an example of \texttt{W2\_EXCH2\_TOPOLOGY.h} and |
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\texttt{w2\_e2setup.F} must reside in a directory containing code |
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linked when \texttt{genmake2} runs. The safest place to put these |
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is the directory indicated in the \texttt{-mods=DIR} command line |
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modifier (typically \texttt{../code}), or the build directory. The |
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default versions of these files reside in \texttt{pkg/exch2}, but |
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they should be left untouched to avoid breaking configurations other |
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than the one you intend to modify.\\ |
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- files containing grid parameters, named |
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\texttt{tile}xxx\texttt{.mitgrid} where xxx is \texttt{001} through |
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\texttt{006}, must be in the working directory when the MITgcm |
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executable is run. These files are provided in the example |
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experiments for cubed sphere configurations with 32$\times$32 cube |
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sides and are non-trivial to generate -- please contact MITgcm |
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support if you want to generate files for other configurations. |
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This is lame. ?? \\ |
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As of the time of writing the following examples use exch2 and may be |
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used for guidance: |
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\begin{verbatim} |
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verification/adjust_nlfs.cs-32x32x1 |
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verification/adjustment.cs-32x32x1 |
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verification/aim.5l_cs |
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verification/global_ocean.cs32x15 |
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verification/hs94.cs-32x32x5 |
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\end{verbatim} |
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\subsection{Generating Topology Files} |
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\subsection{Key Variables} |
\subsection{Key Variables} |
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|
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\texttt{NTILES}, and the maximum number of neighbors of any tiles by |
\texttt{NTILES}, and the maximum number of neighbors of any tiles by |
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\texttt{MAX\_NEIGHBOURS}. These parameters are used for defining the |
\texttt{MAX\_NEIGHBOURS}. These parameters are used for defining the |
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size of the various one and two dimensional arrays that store tile |
size of the various one and two dimensional arrays that store tile |
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parameters indexed to the tile number. |
parameters indexed to the tile number.\\ |
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The scalar parameters \varlink{exch2\_domain\_nxt}{exch2_domain_nxt} |
The scalar parameters \varlink{exch2\_domain\_nxt}{exch2_domain_nxt} |
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and \varlink{exch2\_domain\_nyt}{exch2_domain_nyt} express the number |
and \varlink{exch2\_domain\_nyt}{exch2_domain_nyt} express the number |
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