int MPI_Group_incl(
  MPI_Group group,
  int n,
  int *ranks,
  MPI_Group *newgroup
);

Parameters

group

[in] group (handle)

n

[in] number of elements in array ranks (and size of newgroup ) (integer)

ranks

[in] ranks of processes in group to appear in newgroup (array of integers)

newgroup

[out] new group derived from above, in the order defined by ranks (handle)

Remarks

The function MPI_GROUP_INCL creates a group newgroup that consists of the n processes in group with ranks rank[0], , rank[n-1]; the process with rank i in newgroup is the process with rank ranks[i] in group. Each of the n elements of ranks must be a valid rank in group and all elements must be distinct, or else the program is erroneous. If n~=~0, then newgroup is MPI_GROUP_EMPTY. This function can, for instance, be used to reorder the elements of a group.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS

No error; MPI routine completed successfully.

MPI_ERR_GROUP

Null or invalid group passed to function.

MPI_ERR_ARG

Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

MPI_ERR_INTERN

This error is returned when some part of the MPICH implementation is unable to acquire memory.

MPI_ERR_RANK

Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.

See Also

Example Code

The following sample code illustrates MPI_Group_incl.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
 
int main( int argc, char *argv[] )
{
    MPI_Group g1, g2, g4, g5, g45, selfgroup, g6;
    int ranks[16], size, rank, myrank, range[1][3];
    int errs = 0;
    int i, rin[16], rout[16], result;
 
    MPI_Init(0,0);
 
    MPI_Comm_group( MPI_COMM_WORLD, &g1 );
    MPI_Comm_rank( MPI_COMM_WORLD, &myrank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    if (size < 8) {
        fprintf( stderr, "Test requires 8 processes (16 prefered) only %d provided\n", size ); fflush(stdout);
        MPI_Abort(MPI_COMM_WORLD, 1);
    }
 
    /* 16 members, this process is rank 0, return in group 1 */
    ranks[0] = myrank; ranks[1] = 2; ranks[2] = 7;
    if (myrank == 2) ranks[1] = 3;
    if (myrank == 7) ranks[2] = 6;
    MPI_Group_incl( g1, 3, ranks, &g2 );
 
    /* Check the resulting group */
    MPI_Group_size( g2, &size );
    MPI_Group_rank( g2, &rank );
 
    if (size != 3) {
        fprintf( stderr, "Size should be %d, is %d\n", 3, size );fflush(stderr);
        errs++;
    }
    if (rank != 0) {
        fprintf( stderr, "Rank should be %d, is %d\n", 0, rank );fflush(stderr);
        errs++;
    }
 
    rin[0] = 0; rin[1] = 1; rin[2] = 2;
    MPI_Group_translate_ranks( g2, 3, rin, g1, rout );
    for (i=0; i<3; i++) {
        if (rout[i] != ranks[i]) {
            fprintf( stderr, "translated rank[%d] %d should be %d\n", i, rout[i], ranks[i] );fflush(stderr);
            errs++;
        }
    }
 
    /* Translate the process of the self group against another group */
    MPI_Comm_group( MPI_COMM_SELF, &selfgroup );
    rin[0] = 0;
    MPI_Group_translate_ranks( selfgroup, 1, rin, g1, rout );
    if (rout[0] != myrank) {
        fprintf( stderr, "translated of self is %d should be %d\n", rout[0], myrank );fflush(stderr);
        errs++;
    }
 
    for (i=0; i<size; i++)
        rin[i] = i;
    MPI_Group_translate_ranks( g1, size, rin, selfgroup, rout );
    for (i=0; i<size; i++) {
        if (i == myrank && rout[i] != 0) {
            fprintf( stderr, "translated world to self of %d is %d\n", i, rout[i] );fflush(stderr);
            errs++;
        }
        else if (i != myrank && rout[i] != MPI_UNDEFINED) {
            fprintf( stderr, "translated world to self of %d should be undefined, is %d\n", i, rout[i] );
            errs++;
        }
    }
    MPI_Group_free( &selfgroup );
 
    /* Exclude everyone in our group */
    {
        int i, *ranks, g1size;
 
        MPI_Group_size( g1, &g1size );
 
        ranks = (int *)malloc( g1size * sizeof(int) );
        for (i=0; i<g1size; i++) ranks[i] = i;
        MPI_Group_excl( g1, g1size, ranks, &g6 );
        if (g6 != MPI_GROUP_EMPTY) {
            fprintf( stderr, "Group formed by excluding all ranks not empty\n" );fflush(stderr);
            errs++;
            MPI_Group_free( &g6 );
        }
        free( ranks );
    }
 
    MPI_Group_free( &g2 );
 
    range[0][0] = 1;
    range[0][1] = size-1;
    range[0][2] = 2;
    MPI_Group_range_excl( g1, 1, range, &g5 );
 
    range[0][0] = 1;
    range[0][1] = size-1;
    range[0][2] = 2;
    MPI_Group_range_incl( g1, 1, range, &g4 );
 
    MPI_Group_union( g4, g5, &g45 );
 
    MPI_Group_compare( MPI_GROUP_EMPTY, g4, &result );
    if (result != MPI_UNEQUAL) {
        errs++;
        fprintf( stderr, "Comparison with empty group gave %d, not 3\n", result );fflush(stderr);
    }
    MPI_Group_free( &g4 );
    MPI_Group_free( &g5 );
    MPI_Group_free( &g45 );
 
    /* Now, duplicate the test, but using negative strides */
    range[0][0] = size-1;
    range[0][1] = 1;
    range[0][2] = -2;
    MPI_Group_range_excl( g1, 1, range, &g5 );
 
    range[0][0] = size-1;
    range[0][1] = 1;
    range[0][2] = -2;
    MPI_Group_range_incl( g1, 1, range, &g4 );
 
    MPI_Group_union( g4, g5, &g45 );
 
    MPI_Group_compare( MPI_GROUP_EMPTY, g4, &result );
    if (result != MPI_UNEQUAL) {
        errs++;
        fprintf( stderr, "Comparison with empty group (formed with negative strides) gave %d, not 3\n", result );fflush(stderr);
    }
    MPI_Group_free( &g4 );
    MPI_Group_free( &g5 );
    MPI_Group_free( &g45 );
    MPI_Group_free( &g1 );
 
    MPI_Finalize();
    return 0;
}