5.5.1. Current Practice #1


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Example #1a:

main(int argc, char **argv) 
   { 
     int me, size; 
     ... 
     MPI_Init ( &argc, &argv ); 
     MPI_Comm_rank (MPI_COMM_WORLD, &me); 
     MPI_Comm_size (MPI_COMM_WORLD, &size); 

(void)printf ("Process %d size %d\n", me, size); ... MPI_Finalize(); }

Example #1a is a do-nothing program that initializes itself legally, and refers to the the ``all'' communicator, and prints a message. It terminates itself legally too. This example does not imply that MPI supports printf-like communication itself.

Example #1b (supposing that size is even):

main(int argc, char **argv) 
    { 
       int me, size; 
       int SOME_TAG = 0; 
       ... 
       MPI_Init(&argc, &argv); 

MPI_Comm_rank(MPI_COMM_WORLD, &me); /* local */ MPI_Comm_size(MPI_COMM_WORLD, &size); /* local */

if((me % 2) == 0) { /* send unless highest-numbered process */ if((me + 1) < size) MPI_Send(..., me + 1, SOME_TAG, MPI_COMM_WORLD); } else MPI_Recv(..., me - 1, SOME_TAG, MPI_COMM_WORLD);

... MPI_Finalize(); }

Example #1b schematically illustrates message exchanges between ``even'' and ``odd'' processes in the ``all'' communicator.



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