LAM: What r the soruce and dest rank in both the cases if rank 0 is the calling process in the 2 x 2

On Feb 20, 2007, at 3:50 AM, Rajesh vanaparthi wrote:

> Can anyone explain the following command clearly
>
> MPI_cart_shift (MPI_Comm comm., int direction, int
displ, int *src,  
> int *dest)
>
> Actually this routine finds the resulting source and
destination  
> ranks given the shift direction and displ

Check this out:

http://www.mpi-forum.org/docs/mpi-11-html/node137.
html#Node137

> Please explain me clearly what happens when direction=1
and 0 and  
> also disp < 0, >0 or 0

direction is the dimension of the shift.  For example, in
your 2x2  
example below, direction==0 is dimension 0 (in a C 2D array,
the  
row), and direction==1 is dimension 1 (in a C 2D array, the
column).   
Per the MPI spec, disp==0 is undefined.

> Take the example (let 4 processors are arranged in a 2
x 2 grid  
> with ranks 0 for P(0,0),
> Rank 1 for P(0,1), rank 2 for P(1,0), rank3 for
P(1,1))
>
> If rank 0 is the calling process then please explain me
the  
> following commands
>
> 1)      MPI_Cart_shift(comm., 1, -1, &rsrc,
&rdest);

It depends if the relevant dimensions in comm were marked as
periodic  
or not.

Periodic -- both rsrc and rdest will be 1:

                   |----------------------|
                   |-- 0,0:0 <-- 0,1:1 <--|
                       1,0:2     1,1:3

Non-periodic -- rsrc will be 1 and rdest will be
MPI_PROC_NULL:

     MPI_PROC_NULL <-- 0,0:0 <-- 0,1:1
                       1,0:2     1,1:3

> 2)      MPI_Cart_shift(comm., 0, -1, &rsrc,
&rdest);

Periodic -- both will be 2:

                   |-------|
                   |   0,0:0 --> 0,1:1
                   |       ^
                   |       |
                   |   1,0:2     1,1:3
                   |       ^
                   |-------|

Non-periodic -- rsrc will be 2 and rdest will be
MPI_PROC_NULL:

                      MPI_PROC_NULL
                           ^
                           |
                       0,0:0 --> 0,1:1
                           ^
                           |
                       1,0:2     1,1:3

> What r the soruce and dest rank in both the cases if
rank 0 is the  
> calling process in the 2 x 2 grid
>
>
>        (0,0)
>           0
>
>       (0,1)
>          1
>
>       (1,0)
>          2
>
>      (1,1)
>         3
>
>
>
>
> Here’s a new way to find what you're looking for -
Yahoo! Answers
> _______________________________________________
> This list is archived at http://www.l
am-mpi.org/MailArchives/lam/


-- 
Jeff Squyres
Server Virtualization Business Unit
Cisco Systems


_______________________________________________
This list is archived at http://www.l
am-mpi.org/MailArchives/lam/