MPI_Group_incl

MPI_Group_incl

MPI_Group_incl creates new group from existing group and specifies member processes.

Fortran Syntax

Subroutine MPI_Group_incl(group, count, members, new_group, ierr)

C Syntax

int MPI_Group_incl(MPI_Group group, int count, int *members,
MPI_Group *new_group)

Example in Fortran


      include "mpif.h"
      implicit none
      integer group_world, odd_group, even_group
      integer i, p, Neven, Nodd, members(0:7), ierr

      call MPI_Comm_size(MPI_COMM_WORLD, p, ierr)
      call MPI_Comm_group(MPI_COMM_WORLD,group_world,ierr)

      Neven = (p + 1)/2   ! processes of MPI_COMM_WORLD are divided
      Nodd = p - Neven    ! into odd- and even-numbered groups
      do i=0,Neven - 1    ! "members" determines members of even_group
        members(i) = 2*i
      enddo

      call MPI_Group_incl(group_world, Neven, members, even_group, ierr)

Example in C


  #include "mpi.h";
  MPI_Group group_world, odd_group, even_group;;
  int i, p, Neven, Nodd, members[8], ierr;

  MPI_Comm_size(MPI_COMM_WORLD, &p);
  MPI_Comm_group(MPI_COMM_WORLD, &group_world);

  Neven = (p+1)/2;    /* processes of MPI_COMM_WORLD are divided */
  Nodd = p - Neven;   /* into odd- and even-numbered groups */
  for (i=0; i&#060Neven; i++) {   /* "members" determines members of even_group */
    members[i] = 2*i;
  };

  MPI_Group_incl(group_world, Neven, members, &even_group);

In the above example, we create a new group whose members are the even-numbered processes of the communicator MPI_COMM_WORLD. These group members are ranked in ascending order (0, 1, 2, …, Neven-1) corresponding to the process ranks as defined by (members(0), members(1), …, members(Neven-1)) in the original group (i.e., MPI_COMM_WORLD). In this example, members(0) = 0, members(1) = 2, members(2) = 4, and so on. The same task could also be accomplished by a similar routine, MPI_Group_excl.