Topology
C | Fortran-2008 | Fortran-90
MPI_Group_incl creates a group from a list of process ranks taken from an existing group. If the number of processes to include in the group is 0, the group created is MPI_GROUP_EMPTY. MPI_Group_incl has a variant MPI_Group_range_incl.
int MPI_Group_incl(MPI_Group group,
int rank_count,
const int ranks[],
MPI_Group* new_group);The group to which the process ranks listed belong.
The number of process ranks contained in the list.
An array containing the ranks of the processes in the old group to include in the new group.
The variable in which store the group created. If the number of processes to include in the group is 0, the group created is MPI_GROUP_EMPTY.
The error code returned from the group inclusion.
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
/**
* @brief Illustrates how to create a group by including processes from another
* group.
* @details This application is meant to be run with 4 processes. It begins with
* the default group made of all processes and then creates another group from
* it, keeping only processes 1 and 3.
**/
int main(int argc, char* argv[])
{
MPI_Init(&argc, &argv);
// Check that 4 processes are used
int comm_size;
MPI_Comm_size(MPI_COMM_WORLD, &comm_size);
if(comm_size != 4)
{
printf("This application is meant to be run with 4 processes.\n");
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
// Get the group or processes of the default communicator
MPI_Group world_group;
MPI_Comm_group(MPI_COMM_WORLD, &world_group);
// Get my rank in the world group
int my_world_group_rank;
MPI_Group_rank(world_group, &my_world_group_rank);
// Create the small group by including only processes 1 and 3 from the world group
int small_group_ranks[2] = {1, 3};
MPI_Group small_group;
MPI_Group_incl(world_group, 2, small_group_ranks, &small_group);
// Get my rank in the small group
int my_small_group_rank;
MPI_Group_rank(small_group, &my_small_group_rank);
// Continue only if we are part of the small group
if(my_small_group_rank != MPI_UNDEFINED)
{
printf("I am process %d in world group and %d in small group.\n", my_world_group_rank, my_small_group_rank);
}
else
{
printf("I am process %d in world group but I am not part of the small group.\n", my_world_group_rank);
}
MPI_Finalize();
return EXIT_SUCCESS;
}