RPN_COMM_xch

RPN_COMM

(RPN_COMM_xch_halo)

SUBROUTINE RPN_COMM_xch_halo (g,minx,maxx,miny,maxy,ni,nj,nk,halox,haloy,periodx,periody,gni,npol_row)

ARGUMENTS

g	Array containing the local tile	real or integer	I/O
minx,maxx, miny, maxy	Total dimensions of array g (nk for z axis)	integer	I
ni,nj,nk	Dimensions of local array	integer	I
halox,haloy	Halo width for x and y	integer	I
periodx,periody	Periodicity for x and y	logical	I
gni	Global array size(=problem size) along x	integer	I
npol_row	Number of polar rows of processes (semi-lag case)	integer	I

Dimensions of local array g: g(minx:maxx,miny:maxy,nk)
Dimensions of the local grid: g(1:ni,1:nj,1:nk)
Dimensions of the local grid + halo: g(1-halox:ni+halox,1-haloy:nj+haloy,nk)
Dimensions of a row (semi-lagrangian case): g(gni,nj,nk)

                       maxx
minx +-------------------+ maxy
     |     halo          |
     | +---------------+ |
     | |     ni        | |
     | |             nj| |
     | |(1,1,k)        | |
     | +---------------+ |
     |                   |
     +-------------------+ miny

Size and decomposition of the domain for a 3x3 distribution:

      1        gni
      +--+--+--+
      |P6|P7|P8|
      +--+--+--+
      |P3|P4|P5|
      +--+--+--+
      |P0|P1|P2|
      +--+--+--+
      1         gni

Example of a west-east exchange: the "x" marked column is copied into the halo of the right neighbour.

           P0                                                                    P1
+-----------+                  +-----------+
| halo   x |                  |x halo    |
| +-----+-+ |                  |x+-------+ |
| |      x| |    --------->    |x|       | |
| |      x| |                  |x|       | |
| +-----+-+ |                  |x+-------+ |
| halo   x |                  |x halo    |
+-----------+                  +-----------+

Example of the semi-lagrangian case: here, we put together all local grids of an east-west row of PEs. When the call returns, each PE has the "global" band.

+----------+   +----------+   +----------+    +-------------------+
|    P0    |   |    P1    |   |    P2    |    | P0 et P1 et P2   |
| +------+ |   | +------+ |   | +------+ |    | +---------------+ |
| |xxxxxx| | + | |xxxxxx| | + | |xxxxxx| | -> | |xxxxxxxxxxxxxxx| |
| |xxxxxx| |   | |xxxxxx| |   | |xxxxxx| |    | |xxxxxxxxxxxxxxx| |
| +------+ |   | +------+ |   | +------+ |    | +---------------+ |
|          |   |          |   |          |    |                   |
+----------+   +----------+   +----------+    +-------------------+

N.B.: Obviously, we need minx <= 1-halox < ni+halox <= maxx (same for y)

DESCRIPTION

This subroutine exchange the halos between north, south, east and west neighbours for all PEs. Each PE sends its limitroph band of its local grid to the halo of its neighbour. The size of the limitroph band is specified by halox and haloy.

If npol_row > 0, then the semi-lagrangian exchange will be used for the npol_row rows of PEs at the northern and southern extremity of the domain.

EXEMPLE

call rpn_comm_xch_halo(tableau,minx,maxx,miny,maxy,ni,nj,nk,1,1,periodx, periody,gni,npol_row)

RPN_COMM

(RPN_COMM_xch_halo)

ARGUMENTS

DESCRIPTION

EXEMPLE

SEE ALSO