--- manual/s_phys_pkgs/text/exch2.tex	2004/05/10 21:39:11	1.19
+++ manual/s_phys_pkgs/text/exch2.tex	2005/07/18 20:45:27	1.24
@@ -1,4 +1,4 @@
-% $Header: /home/ubuntu/mnt/e9_copy/manual/s_phys_pkgs/text/exch2.tex,v 1.19 2004/05/10 21:39:11 afe Exp $
+% $Header: /home/ubuntu/mnt/e9_copy/manual/s_phys_pkgs/text/exch2.tex,v 1.24 2005/07/18 20:45:27 molod Exp $
 % $Name:  $
 
 %%  * Introduction
@@ -10,11 +10,11 @@
 %%    o automatically inserted at \section{Reference} 
 
 
-\section{exch2: Extended Cubed Sphere \mbox{Topology}}
+\subsection{exch2: Extended Cubed Sphere \mbox{Topology}}
 \label{sec:exch2}
 
 
-\subsection{Introduction}
+\subsubsection{Introduction}
 
 The \texttt{exch2} package extends the original cubed sphere topology
 configuration to allow more flexible domain decomposition and
@@ -41,7 +41,7 @@
 \file{utils/exch2/code-mods} along with the appropriate \file{SIZE.h}
 file for single-processor execution.
 
-\subsection{Invoking exch2}
+\subsubsection{Invoking exch2}
 
 To use exch2 with the cubed sphere, the following conditions must be
 met: \\
@@ -96,7 +96,7 @@
 
 
 
-\subsection{Generating Topology Files for exch2}
+\subsubsection{Generating Topology Files for exch2}
 \label{sec:topogen}
 
 Alternate cubed sphere topologies may be created using the Matlab
@@ -182,7 +182,7 @@
 
 
 
-\subsection{exch2, SIZE.h, and Multiprocessing}
+\subsubsection{exch2, SIZE.h, and Multiprocessing}
 \label{sec:exch2mpi}
 
 Once the topology configuration files are created, the Fortran
@@ -215,12 +215,20 @@
 The number of tiles MITgcm allocates and how they are distributed
 between processors depends on \varlink{nPx}{nPx} and
 \varlink{nSx}{nSx}.  \varlink{nSx}{nSx} is the number of tiles per
-processor and \varlink{nPx}{nPx} is the number of processors.  The total
-number of tiles in the topology minus those listed in
-\file{blanklist.txt} must equal \code{nSx*nPx}.  Note that in order to 
+processor and \varlink{nPx}{nPx} is the number of processors.  The
+total number of tiles in the topology minus those listed in
+\file{blanklist.txt} must equal \code{nSx*nPx}.  Note that in order to
 obtain maximum usage from a given number of processors in some cases,
-this restriction might entail sharing a processor with a tile that would 
-otherwise be excluded. \\
+this restriction might entail sharing a processor with a tile that
+would otherwise be excluded because it is topographically outside of
+the domain and therefore in \file{blanklist.txt}.  For example,
+suppose you have five processors and a domain decomposition of
+thirty-six tiles that allows you to exclude seven tiles.  To evenly
+distribute the remaining twenty-nine tiles among five processors, you
+would have to run one ``dummy'' tile to make an even six tiles per
+processor.  Such dummy tiles are \emph{not} listed in
+\file{blanklist.txt}.\\
+
 
 The following is an example of \file{SIZE.h} for the twelve-tile
 configuration illustrated in figure \ref{fig:12tile} running on 
@@ -263,7 +271,7 @@
 
 
 
-\subsection{Key Variables}
+\subsubsection{Key Variables}
 
 The descriptions of the variables are divided up into scalars,
 one-dimensional arrays indexed to the tile number, and two and
@@ -273,7 +281,7 @@
 arrays to individual tiles, and the arrays indexed by tile and
 neighbor to relationships between tiles and their neighbors. \\
 
-\subsubsection{Scalars}
+Scalars:
 
 The number of tiles in a particular topology is set with the parameter
 \code{NTILES}, and the maximum number of neighbors of any tiles by
@@ -296,7 +304,7 @@
 $x$ axis, and the $y$ axis variable \varlink{bj}{bj} is assumed to 
 equal \code{1} throughout the package. \\
 
-\subsubsection{Arrays indexed to tile number}
+Arrays indexed to tile number:
 
 The following arrays are of length \code{NTILES} and are indexed to
 the tile number, which is indicated in the diagrams with the notation
@@ -349,7 +357,7 @@
 corners of the cube. \\
 
 
-\subsubsection{Arrays Indexed to Tile Number and Neighbor}
+Arrays Indexed to Tile Number and Neighbor:
 
 The following arrays have vectors of length \code{MAX\_NEIGHBOURS} and
 \code{NTILES} and describe the orientations between the the tiles. \\
@@ -493,7 +501,7 @@
 width of \code{T}'s northern edge, expanded by one into the halo. \\
 
 
-\subsection{Key Routines}
+\subsubsection{Key Routines}
 
 Most of the subroutines particular to exch2 handle the exchanges
 themselves and are of the same format as those described in
