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--- manual/s_phys_pkgs/text/exch2.tex 2004/01/29 15:39:49 1.3
+++ manual/s_phys_pkgs/text/exch2.tex 2004/01/29 17:55:35 1.4
@@ -1,4 +1,4 @@
-% $Header: /home/ubuntu/mnt/e9_copy/manual/s_phys_pkgs/text/exch2.tex,v 1.3 2004/01/29 15:39:49 afe Exp $
+% $Header: /home/ubuntu/mnt/e9_copy/manual/s_phys_pkgs/text/exch2.tex,v 1.4 2004/01/29 17:55:35 afe Exp $
% $Name: $
%% * Introduction
@@ -18,14 +18,107 @@
The exch2 package is an extension to the original cubed sphere exchanges
to allow more flexible domain decomposition and parallelization. Cube faces
-(subdomain) may be divided into whatever number of tiles that divide evenly
+(subdomains) may be divided into whatever number of tiles that divide evenly
into the grid point dimensions of the subdomain. Furthermore, the individual
-tiles may be run on different processors in any combination, (tone this down
-a bit), and whether exchanges between particular tiles occur between different
-processors is decided at runtime.
-
-
-
+tiles may be run on separate processors in different combinations,
+and whether exchanges between particular tiles occur between different
+processors is determined at runtime.
+
+The exchange parameters are declared in {\em W2\_EXCH2\_TOPOLOGY.h} and
+assigned in {\em w2\_e2setup.F}, both in the
+{\em pkg/exch2} directory. The validity of the cube topology depends
+on the {\em SIZE.h} file as detailed below. Both files are generated by
+Matlab scripts and
+should not be edited. The default files provided in the release set up
+a cube sphere arrangement of six tiles, one per subdomain, each with 32x32 grid
+points, running on a single processor.
+
+\subsection{Key Variables}
+
+The descriptions of the variables are divided up into scalars,
+one-dimensional arrays indexed to the tile number, and two-dimensional
+arrays indexed to tile number and neighboring tile. This division
+actually reflects the functionality of these variables, not just the
+whim of some FORTRAN enthusiast.
+
+\subsubsection{Scalars}
+
+The number of tiles in a particular topology is set with the parameter
+{\em NTILES}, and the maximum number of neighbors of any tiles by
+{\em MAX\_NEIGHBOURS}. These parameters are used for defining the size of
+the various one and two dimensional arrays that store tile parameters
+indexed to the tile number.
+
+The scalar parameters {\em exch2\_domain\_nxt} and
+{\em exch2\_domain\_nyt} express the number of tiles in the x and y global
+indices. For example, the default setup of six tiles has
+{\em exch2\_domain\_nxt=6} and {\em exch2\_domain\_nyt=1}. A topology of
+twenty-four square (in gridpoints) tiles, four (2x2) per subdomain, will
+have {\em exch2\_domain\_nxt=12} and {\em exch2\_domain\_nyt=2}. Note
+that these parameters express the tile layout to allow global data files that
+are tile-layout-neutral and have no bearing on the internal storage of the
+arrays. The tiles are internally stored in a range from {\em 1,bi} (in the
+x axis) and y-axis variable {\em bj} is generally ignored within the package.
+
+\subsubsection{One-Dimensional Arrays}
+
+The following arrays are indexed to the tile number, and the indices are
+omitted in their descriptions.
+
+The arrays {\em exch2\_tnx} and {\em exch2\_tny}
+express the x and y dimensions of each tile. At present for each tile
+{\em exch2\_tnx = sNx}
+and {\em exch2\_tny = sNy}, as assigned in {\em SIZE.h}. Future releases of
+MITgcm are to allow varying tile sizes.
+
+The location of the tiles' Cartesian origin within a subdomain are determined
+by the arrays {\em exch2\_tbasex} and {\em exch2\_tbasey}. These
+
+\subsubsection{Two-Dimensional Arrays}
+
+
+//
+
+\begin{verbatim}
+C NTILES :: Number of tiles in this topology
+C MAX_NEIGHBOURS :: Maximum number of neighbours any tile has.
+C exch2_domain_nxt :: Total domain length in tiles.
+C exch2_domain_nyt :: Maximum domain height in tiles.
+C exch2_tnx :: Size in X for each tile.
+C exch2_tny :: Size in Y for each tile.
+C exch2_tbasex :: Tile offset in X within its sub-domain (cube face)
+C exch2_tbasey :: Tile offset in Y within its sub-domain (cube face)
+C exch2_tglobalxlo :: Tile base X index within global index space.
+C exch2_tglobalylo :: Tile base Y index within global index space.
+C exch2_isWedge :: 0 if West not at domain edge, 1 if it is.
+C exch2_isNedge :: 0 if North not at domain edge, 1 if it is.
+C exch2_isEedge :: 0 if East not at domain edge, 1 if it is.
+C exch2_isSedge :: 0 if South not at domain edge, 1 if it is.
+C exch2_myFace :: Cube face number used for I/O.
+C exch2_nNeighbours :: Tile neighbour entries count.
+C exch2_tProc :: Rank of process owning tile
+C :: (filled at run time).
+C exch2_neighbourId :: Tile number for each neighbour entry.
+C exch2_opposingSend_record :: Record for entry in target tile send
+C :: list that has this tile and face
+C :: as its target.
+C exch2_pi :: X index row of target to source permutation
+C :: matrix for each neighbour entry.
+C exch2_pj :: Y index row of target to source permutation
+C :: matrix for each neighbour entry.
+C exch2_oi :: X index element of target to source
+C :: offset vector for cell-centered quantities
+C :: of each neighbor entry.
+C exch2_oj :: Y index element of target to source
+C :: offset vector for cell-centered quantities
+C :: of each neighbor entry.
+C exch2_oi_f :: X index element of target to source
+C :: offset vector for face quantities
+C :: of each neighbor entry.
+C exch2_oj_f :: Y index element of target to source
+C :: offset vector for face quantities
+C :: of each neighbor entry.
+\end{verbatim}
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