5 #define MAX_PROCESSES 10
7 int main( int argc, char **argv )
10 int table[MAX_PROCESSES][MAX_PROCESSES];
15 MPI_Init( &argc, &argv );
16 MPI_Comm_rank( MPI_COMM_WORLD, &rank );
17 MPI_Comm_size( MPI_COMM_WORLD, &size );
19 /* A maximum of MAX_PROCESSES processes can participate */
20 if ( size > MAX_PROCESSES ) participants = MAX_PROCESSES;
21 else participants = size;
22 /* Set the particpants so that it divides the MAX_PROCESSES */
23 while (MAX_PROCESSES % participants) participants--;
24 /* Create the communicator */
25 MPI_Comm_split( MPI_COMM_WORLD, rank < participants, rank, &testcomm );
27 if (MAX_PROCESSES % participants) {
28 fprintf( stderr, "Number of processors must divide %d\n",
30 MPI_Abort( MPI_COMM_WORLD, 1 );
32 if ( (rank < participants) ) {
34 /* Determine what rows are my responsibility */
35 int block_size = MAX_PROCESSES / participants;
36 int begin_row = rank * block_size;
37 int end_row = (rank+1) * block_size;
38 int send_count = block_size * MAX_PROCESSES;
39 int recv_count = send_count;
41 /* Paint my rows my color */
42 for (i=begin_row; i<end_row ;i++)
43 for (j=0; j<MAX_PROCESSES; j++)
44 table[i][j] = rank + 10;
46 /* Gather everybody's result together - sort of like an */
47 /* inefficient allgather */
48 for (i=0; i<participants; i++)
49 MPI_Gather(&table[begin_row][0], send_count, MPI_INT,
50 &table[0][0], recv_count, MPI_INT, i,
53 /* Everybody should have the same table now, */
54 /* This test does not in any way guarantee there are no errors */
55 /* Print out a table or devise a smart test to make sure it's correct */
56 for (i=0; i<MAX_PROCESSES;i++) {
57 if ( (table[i][0] - table[i][MAX_PROCESSES-1] !=0) )
62 MPI_Comm_free( &testcomm );
66 printf( "[%d] done with ERRORS(%d)!\n", rank, errors );