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revision 1.5 by afe, Thu Jan 29 21:03:53 2004 UTC revision 1.8 by edhill, Tue Feb 17 21:58:56 2004 UTC
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10  %%    o automatically inserted at \section{Reference}  %%    o automatically inserted at \section{Reference}
11    
12    
13  \section{exch2: Extended Cubed Sphere Exchange}  \section{Extended Cubed Sphere Exchange}
14  \label{sec:exch2}  \label{sec:exch2}
15    
16    
17  \subsection{Introduction}  \subsection{Introduction}
18    
19  The exch2 package is an extension to the original cubed sphere exchanges  The \texttt{exch2} package is an extension to the original cubed
20  to allow more flexible domain decomposition and parallelization.  Cube faces  sphere exchanges to allow more flexible domain decomposition and
21  (subdomains) may be divided into whatever number of tiles that divide evenly  parallelization.  Cube faces (subdomains) may be divided into whatever
22  into the grid point dimensions of the subdomain.  Furthermore, the individual  number of tiles that divide evenly into the grid point dimensions of
23  tiles may be run on separate processors in different combinations,  the subdomain.  Furthermore, the individual tiles may be run on
24  and whether exchanges between particular tiles occur between different  separate processors in different combinations, and whether exchanges
25  processors is determined at runtime.  between particular tiles occur between different processors is
26    determined at runtime.
27  The exchange parameters are declared in {\em W2\_EXCH2\_TOPOLOGY.h} and  
28  assigned in {\em w2\_e2setup.F}, both in the  The exchange parameters are declared in
29  {\em pkg/exch2} directory.  The validity of the cube topology depends  \filelink{pkg/exch2/W2\_EXCH2\_TOPOLOGY.h}{pkg-exch2-W2_EXCH2_TOPOLOGY.h}
30  on the {\em SIZE.h} file as detailed below.  Both files are generated by  and assigned in
31  Matlab scripts and  \filelink{pkg/exch2/w2\_e2setup.F}{pkg-exch2-w2_e2setup.F}, both in
32  should not be edited.  The default files provided in the release set up  the \texttt{pkg/exch2} directory.  The validity of the cube topology
33  a cube sphere arrangement of six tiles, one per subdomain, each with 32x32 grid  depends on the \texttt{SIZE.h} file as detailed below.  Both files are
34  points, running on a single processor.    generated by Matlab scripts and should not be edited.  The default
35    files provided in the release set up a cube sphere arrangement of six
36    tiles, one per subdomain, each with 32x32 grid points, running on a
37    single processor.
38    
39  \subsection{Key Variables}  \subsection{Key Variables}
40    
41  The descriptions of the variables are divided up into scalars,  The descriptions of the variables are divided up into scalars,
42  one-dimensional arrays indexed to the tile number, and two-dimensional  one-dimensional arrays indexed to the tile number, and two and three
43  arrays indexed to tile number and neighboring tile.  This division  dimensional arrays indexed to tile number and neighboring tile.  This
44  actually reflects  the functionality of these variables, not just the  division actually reflects the functionality of these variables: the
45  whim of some FORTRAN enthusiast.  scalars are common to every part of the topology, the tile-indexed
46    arrays to individual tiles, and the arrays indexed to tile and
47    neighbor to relationships between tiles and their neighbors.
48    
49  \subsubsection{Scalars}  \subsubsection{Scalars}
50    
51  The number of tiles in a particular topology is set with the parameter  The number of tiles in a particular topology is set with the parameter
52  {\em NTILES}, and the maximum number of neighbors of any tiles by  \texttt{NTILES}, and the maximum number of neighbors of any tiles by
53  {\em MAX\_NEIGHBOURS}.  These parameters are used for defining the size of  \texttt{MAX\_NEIGHBOURS}.  These parameters are used for defining the
54  the various one and two dimensional arrays that store tile parameters  size of the various one and two dimensional arrays that store tile
55  indexed to the tile number.  parameters indexed to the tile number.
56    
57  The scalar parameters {\em exch2\_domain\_nxt} and  The scalar parameters \varlink{exch2\_domain\_nxt}{exch2_domain_nxt}
58  {\em exch2\_domain\_nyt} express the number of tiles in the x and y global  and \varlink{exch2\_domain\_nyt}{exch2_domain_nyt} express the number
59  indices.  For example, the default setup of six tiles has  of tiles in the x and y global indices.  For example, the default
60  {\em exch2\_domain\_nxt=6} and {\em exch2\_domain\_nyt=1}.  A topology of  setup of six tiles has \texttt{exch2\_domain\_nxt=6} and
61  twenty-four square (in gridpoints) tiles, four (2x2) per subdomain, will  \texttt{exch2\_domain\_nyt=1}.  A topology of twenty-four square (in
62  have {\em exch2\_domain\_nxt=12} and {\em exch2\_domain\_nyt=2}.  Note  gridpoints) tiles, four (2x2) per subdomain, will have
63  that these parameters express the tile layout to allow global data files that  \texttt{exch2\_domain\_nxt=12} and \texttt{exch2\_domain\_nyt=2}.
64  are tile-layout-neutral and have no bearing on the internal storage of the  Note that these parameters express the tile layout to allow global
65  arrays.  The tiles are internally stored in a range from {\em 1,bi} (in the  data files that are tile-layout-neutral and have no bearing on the
66  x axis) and y-axis variable {\em bj} is generally ignored within the package.  internal storage of the arrays.  The tiles are internally stored in a
67    range from \texttt{1,bi} (in the x axis) and y-axis variable
68  \subsubsection{One-Dimensional Arrays}  \texttt{bj} is generally ignored within the package.
69    
70  The following arrays are of size {\em NTILES}, are indexed to the tile number,  \subsubsection{Arrays Indexed to Tile Number}
71  and the indices are omitted in their descriptions.  
72    The following arrays are of size \texttt{NTILES}, are indexed to the
73  The arrays {\em exch2\_tnx} and {\em exch2\_tny}  tile number, and the indices are omitted in their descriptions.
74  express the x and y dimensions of each tile.  At present for each tile  
75  {\em exch2\_tnx = sNx}  The arrays \varlink{exch2\_tnx}{exch2_tnx} and
76  and {\em exch2\_tny = sNy}, as assigned in {\em SIZE.h}.  Future releases of  \varlink{exch2\_tny}{exch2_tny} express the x and y dimensions of each
77  MITgcm are to allow varying tile sizes.  tile.  At present for each tile \texttt{exch2\_tnx=sNx} and
78    \texttt{exch2\_tny=sNy}, as assigned in \texttt{SIZE.h}.  Future
79  The location of the tiles' Cartesian origin within a subdomain are determined  releases of MITgcm are to allow varying tile sizes.
80  by the arrays {\em exch2\_tbasex} and {\em exch2\_tbasey}.  These variables  
81  are used to relate the location of the edges of the tiles to each other.  As  The location of the tiles' Cartesian origin within a subdomain are
82  an example, in the default six-tile topology (the degenerate case)  determined by the arrays \varlink{exch2\_tbasex}{exch2_tbasex} and
83  each index in these arrays are  \varlink{exch2\_tbasey}{exch2_tbasey}.  These variables are used to
84  set to 0.  The twenty-four, 32x32 cube face case discussed above will have  relate the location of the edges of the tiles to each other.  As an
85  values of 0 or 16, depending on the quadrant the tile falls within the  example, in the default six-tile topology (the degenerate case) each
86  subdomain.  {\em exch2\_myFace} contains the number of the  index in these arrays are set to 0.  The twenty-four, 32x32 cube face
87  cubeface/subdomain of each tile, numbered 1-6 in the case of the standard  case discussed above will have values of 0 or 16, depending on the
88  cube topology.    quadrant the tile falls within the subdomain.  The array
89    \varlink{exch2\_myFace}{exch2_myFace} contains the number of the
90  The arrays {\em exch2\_txglobalo} and {\em exch2\_txglobalo} are similar to  cubeface/subdomain of each tile, numbered 1-6 in the case of the
91  {\em exch2\_tbasex} and {\em exch2\_tbasey}, but locate the tiles within  standard cube topology.
92  the global address space, similar to that used by global files.    
93    The arrays \varlink{exch2\_txglobalo}{exch2_txglobalo} and
94  The arrays {\em exch2\_isWedge}, {\em exch2\_isEedge}, {\em exch2\_isSedge},  \varlink{exch2\_txglobalo}{exch2_txglobalo} are similar to
95  and {\em exch2\_isNedge} are set to 1 if the indexed tile lies on the edge  \varlink{exch2\_tbasex}{exch2_tbasex} and
96  of a subdomain, 0 if not.  The values are used within the topology generator  \varlink{exch2\_tbasey}{exch2_tbasey}, but locate the tiles within the
97  to determine the orientation of neighboring tiles and to indicate whether  global address space, similar to that used by global files.
98  a tile lies on the corner of a subdomain.  The latter case indicates  
99  special exchange and numerical handling for the singularities at the eight  The arrays \varlink{exch2\_isWedge}{exch2_isWedge},
100  corners of the cube.  {\em exch2\_isNedge} contains a count of how many  \varlink{exch2\_isEedge}{exch2_isEedge},
101  neighboring tiles each tile has, and is used for setting bounds for looping  \varlink{exch2\_isSedge}{exch2_isSedge}, and
102  over neighboring tiles.  {\em exch2\_tProc} holds the process rank of each tile,  \varlink{exch2\_isNedge}{exch2_isNedge} are set to 1 if the indexed
103  and is used in interprocess communication.  tile lies on the edge of a subdomain, 0 if not.  The values are used
104    within the topology generator to determine the orientation of
105  \subsubsection{Two-Dimensional Arrays}  neighboring tiles and to indicate whether a tile lies on the corner of
106    a subdomain.  The latter case indicates special exchange and numerical
107  The following arrays are all of size {\em MAX\_NEIGHBOURS}x{\em NTILES} and  handling for the singularities at the eight corners of the cube.
108  describe the orientations between the the tiles.  \varlink{exch2\_nNeighbours}{exch2_nNeighbours} contains a count of
109    how many neighboring tiles each tile has, and is used for setting
110  The array {\em exch2\_neighbourId(a,T)} holds the tile number $T_{n}$ for each tile  bounds for looping over neighboring tiles.
111  {\em T}'s neighbor tile {\em a}, and {\em exch2\_opposingSend\_record(a,T)} holds  \varlink{exch2\_tProc}{exch2_tProc} holds the process rank of each
112  the index c in {\em exch2\_neighbourId(b,$T_{n}$)} that holds the tile number T.  tile, and is used in interprocess communication.
113  In other words,  
114    \subsubsection{Arrays Indexed to Tile Number and Neighbor}
115  \begin{verbatim}    
116  exch2_neighbourId( exch2_opposingSend_record(a,T), exch2_neighbourId(a,T) ) = T  The following arrays are all of size \texttt{MAX\_NEIGHBOURS} $\times$
117    \texttt{NTILES} and describe the orientations between the the tiles.
118    
119    The array \texttt{exch2\_neighbourId(a,T)} holds the tile number for
120    each of the $n$ neighboring tiles.  The neighbor tiles are indexed
121    \texttt{(1,MAX\_NEIGHBOURS} in the order right to left on the north
122    then south edges, and then top to bottom on the east and west edges.
123    Maybe throw in a fig here, eh?
124    
125    The \texttt{exch2\_opposingSend\_record(a,T)} array holds the index c
126    in \texttt{exch2\_neighbourId(b,$T_{n}$)} that holds the tile number T.
127    In other words,
128    \begin{verbatim}
129       exch2_neighbourId( exch2_opposingSend_record(a,T),
130                          exch2_neighbourId(a,T) ) = T
131  \end{verbatim}  \end{verbatim}
132    and this provides a back-reference from the neighbor tiles.
133    
134  {\em exch2\_neighbourId(exch2\_opposingSend\_record(a,T),exch2\_neighbourId(a,T))=T}.  The arrays \varlink{exch2\_pi}{exch2_pi},
135  This is to provide a backreference from the neighbor tiles.  \varlink{exch2\_pj}{exch2_pj}, \varlink{exch2\_oi}{exch2_oi},
136    \varlink{exch2\_oj}{exch2_oj}, \varlink{exch2\_oi\_f}{exch2_oi_f}, and
137    \varlink{exch2\_oj\_f}{exch2_oj_f} specify the transformations in
138    exchanges between the neighboring tiles.  The dimensions of
139    \texttt{exch2\_pi(t,N,T)} and \texttt{exch2\_pj(t,N,T)} are the
140    neighbor ID \textit{N} and the tile number \textit{T} as explained
141    above, plus the transformation vector {\em t }, of length two.  The
142    first element of the transformation vector indicates the factor by
143    which variables representing the same vector component of a tile will
144    be multiplied, and the second element indicates the transform to the
145    variable in the other direction.  As an example,
146    \texttt{exch2\_pi(1,N,T)} holds the transform of the i-component of a
147    vector variable in tile \texttt{T} to the i-component of tile
148    \texttt{T}'s neighbor \texttt{N}, and \texttt{exch2\_pi(2,N,T)} hold
149    the component of neighbor \texttt{N}'s j-component.
150    
151    Under the current cube topology, one of the two elements of
152    \texttt{exch2\_pi} or \texttt{exch2\_pj} for a given tile \texttt{T}
153    and neighbor \texttt{N} will be 0, reflecting the fact that the vector
154    components are orthogonal.  The other element will be 1 or -1,
155    depending on whether the components are indexed in the same or
156    opposite directions.  For example, the transform dimension of the
157    arrays for all tile neighbors on the same subdomain will be [1,0],
158    since all tiles on the same subdomain are oriented identically.
159    Vectors that correspond to the orthogonal dimension with the same
160    index direction will have [0,1], whereas those in the opposite index
161    direction will have [0,-1].
162    
 //  
163    
164    {\footnotesize
165  \begin{verbatim}  \begin{verbatim}
   
   
 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.                        
166  C      exch2_pi          :: X index row of target to source permutation  C      exch2_pi          :: X index row of target to source permutation
167  C                        :: matrix for each neighbour entry.              C                        :: matrix for each neighbour entry.            
168  C      exch2_pj          :: Y index row of target to source permutation  C      exch2_pj          :: Y index row of target to source permutation
# Line 141  C      exch2_oj_f        :: Y index elem Line 180  C      exch2_oj_f        :: Y index elem
180  C                        :: offset vector for face quantities            C                        :: offset vector for face quantities          
181  C                        :: of each neighbor entry.                      C                        :: of each neighbor entry.                    
182  \end{verbatim}  \end{verbatim}
183    }
184    
185    
186    
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