int MPI_Group_range_excl(
  MPI_Group group,
  int n,
  int ranges[][3], 
  MPI_Group *newgroup
);

Parameters

group

[in] group (handle)

n

[in] number of elements in array ranks (integer)

ranges

[in] a one-dimensional array of integer triplets of the form (first rank, last rank, stride), indicating the ranks in group of processes to be excluded from the output group newgroup .

newgroup

[out] new group derived from above, preserving the order in group (handle)

Remarks

The functionality of this routine is specified to be equivalent to expanding the array of ranges to an array of the excluded ranks and passing the resulting array of ranks and other arguments to MPI_GROUP_EXCL. A call to MPI_GROUP_EXCL is equivalent to a call to MPI_GROUP_RANGE_EXCL with each rank i in ranks replaced by the triplet (i,i,1) in the argument ranges.

Advice to users.

The range operations do not explicitly enumerate ranks, and therefore are more scalable if implemented efficiently. Hence, we recommend MPI programmers to use them whenenever possible, as high-quality implementations will take advantage of this fact.

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_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.

MPI_ERR_ARG

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

See Also

Example Code

The following sample code illustrates MPI_Group_range_excl.

/*
Test the group routines
MPI_Group_compare
MPI_Group_excl
MPI_Group_intersection
MPI_Group_range_excl
MPI_Group_rank
MPI_Group_size
MPI_Group_translate_ranks
MPI_Group_union
*/
#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
 
int main( int argc, char **argv )
{
    int errs=0, toterr;
    MPI_Group basegroup;
    MPI_Group g1, g2, g3, g4, g5, g6, g7, g8, g9, g10;
    MPI_Group g3a, g3b;
    MPI_Comm comm, newcomm, splitcomm, dupcomm;
    int i, grp_rank, rank, grp_size, size, result;
    int nranks, *ranks, *ranks_out;
    int range[1][3];
    int worldrank;
 
    MPI_Init( &argc, &argv );
    MPI_Comm_rank( MPI_COMM_WORLD, &worldrank );
    comm = MPI_COMM_WORLD;
    MPI_Comm_group( comm, &basegroup );
    MPI_Comm_rank( comm, &rank );
    MPI_Comm_size( comm, &size );
 
    /* Get the basic information on this group */
    MPI_Group_rank( basegroup, &grp_rank );
    if (grp_rank != rank) {
        errs++;
        fprintf( stdout, "group rank %d != comm rank %d\n", grp_rank, rank );fflush(stdout);
    }
    MPI_Group_size( basegroup, &grp_size );
    if (grp_size != size) {
        errs++;
        fprintf( stdout, "group size %d != comm size %d\n", grp_size, size );
    }
 
    /* Form a new communicator with inverted ranking */
    MPI_Comm_split( comm, 0, size - rank, &newcomm );
    MPI_Comm_group( newcomm, &g1 );
    ranks = (int *)malloc( size * sizeof(int) );
    ranks_out = (int *)malloc( size * sizeof(int) );
    for (i=0; i<size; i++) ranks[i] = i;
    nranks = size;
    MPI_Group_translate_ranks( g1, nranks, ranks, basegroup, ranks_out );
    for (i=0; i<size; i++) {
        if (ranks_out[i] != (size - 1) - i) {
            errs++;
            fprintf( stdout, "Translate ranks got %d expected %d\n", ranks_out[i], (size - 1) - i );fflush(stdout);
        }
    }
 
    /* Check Compare */
    MPI_Group_compare( basegroup, g1, &result );
    if (result != MPI_SIMILAR) {
        errs++;
        fprintf( stdout, "Group compare should have been similar, was %d\n", result );fflush(stdout);
    }
    MPI_Comm_dup( comm, &dupcomm );
    MPI_Comm_group( dupcomm, &g2 );
    MPI_Group_compare( basegroup, g2, &result );
    if (result != MPI_IDENT) {
        errs++;
        fprintf( stdout, "Group compare should have been ident, was %d\n", result );fflush(stdout);
    }
    MPI_Comm_split( comm, rank < size/2, rank, &splitcomm );
    MPI_Comm_group( splitcomm, &g3 );
    MPI_Group_compare( basegroup, g3, &result );
    if (result != MPI_UNEQUAL) {
        errs++;
        fprintf( stdout, "Group compare should have been unequal, was %d\n", result );fflush(stdout);
    }
 
    /* Build two groups that have this process and one other, but do not have the same processes */
    ranks[0] = rank;
    ranks[1] = (rank + 1) % size;
    MPI_Group_incl( basegroup, 2, ranks, &g3a );
    ranks[1] = (rank + size - 1) % size;
    MPI_Group_incl( basegroup, 2, ranks, &g3b );
    MPI_Group_compare( g3a, g3b, &result );
    if (result != MPI_UNEQUAL) {
        errs++;
        fprintf( stdout, "Group compare of equal sized but different groups should have been unequal, was %d\n", result );fflush(stdout);
    }

    /* Build two new groups by excluding members; use Union to put them together again */
    /* Exclude 0 */
    for (i=0; i<size; i++) ranks[i] = i;
    MPI_Group_excl( basegroup, 1, ranks, &g4 );
    /* Exclude 1-(size-1) */
    MPI_Group_excl( basegroup, size-1, ranks+1, &g5 );
    MPI_Group_union( g5, g4, &g6 );
    MPI_Group_compare( basegroup, g6, &result );
    if (result != MPI_IDENT) {
        int usize;
        errs++;
        /* See ordering requirements on union */
        fprintf( stdout, "Group excl and union did not give ident groups\n" );
        fprintf( stdout, "[%d] result of compare was %d\n", rank, result );
        MPI_Group_size( g6, &usize );
        fprintf( stdout, "Size of union is %d, should be %d\n", usize, size );
        fflush(stdout);
    }
    MPI_Group_union( basegroup, g4, &g7 );
    MPI_Group_compare( basegroup, g7, &result );
    if (result != MPI_IDENT) {
        int usize;
        errs++;
        fprintf( stdout, "Group union of overlapping groups failed\n" );
        fprintf( stdout, "[%d] result of compare was %d\n", rank, result );
        MPI_Group_size( g7, &usize );
        fprintf( stdout, "Size of union is %d, should be %d\n", usize, size );
        fflush(stdout);
    }
 
    /* Use range_excl instead of ranks */
    /* printf ("range excl\n" ); fflush( stdout ); */
    range[0][0] = 1;
    range[0][1] = size-1;
    range[0][2] = 1;
    MPI_Group_range_excl( basegroup, 1, range, &g8 );
    /* printf( "out of range excl\n" ); fflush( stdout ); */
    MPI_Group_compare( g5, g8, &result );
    /* printf( "out of compare\n" ); fflush( stdout ); */
    if (result != MPI_IDENT) {
        errs++;
        fprintf( stdout, "Group range excl did not give ident groups\n" );
    }
 
    /* printf( "intersection\n" ); fflush( stdout ); */
    MPI_Group_intersection( basegroup, g4, &g9 );
    MPI_Group_compare( g9, g4, &result );
    if (result != MPI_IDENT) {
        errs++;
        fprintf( stdout, "Group intersection did not give ident groups\n" );
    }
 
    /* Exclude EVERYTHING and check against MPI_GROUP_EMPTY */
    /* printf( "range excl all\n" ); fflush( stdout ); */
    range[0][0] = 0;
    range[0][1] = size-1;
    range[0][2] = 1;
    MPI_Group_range_excl( basegroup, 1, range, &g10 );
 
    MPI_Group_compare( g10, MPI_GROUP_EMPTY, &result );
 
    if (result != MPI_IDENT) {
        errs++;
        fprintf( stdout, "MPI_GROUP_EMPTY didn't compare against empty group\n");fflush(stdout);
    }
 
    MPI_Group_free( &basegroup );
    MPI_Group_free( &g1 );
    MPI_Group_free( &g2 );
    MPI_Group_free( &g3 );
    MPI_Group_free( &g3a );
    MPI_Group_free( &g3b );
    MPI_Group_free( &g4 );
    MPI_Group_free( &g5 );
    MPI_Group_free( &g6 );
    MPI_Group_free( &g7 );
    MPI_Group_free( &g8 );
    MPI_Group_free( &g9 );
    MPI_Group_free( &g10 );
    MPI_Comm_free( &dupcomm );
    MPI_Comm_free( &splitcomm );
    MPI_Comm_free( &newcomm );
 
    MPI_Finalize();
    return errs;
}