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45 lines
1.1 KiB
45 lines
1.1 KiB
#include "mpi.h"
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#include <stdio.h>
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#define NPROCS 8
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int main(argc,argv)
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int argc;
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char *argv[]; {
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int rank, new_rank, sendbuf, recvbuf, numtasks,
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ranks1[4]={0,1,2,3}, ranks2[4]={4,5,6,7};
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MPI_Group orig_group, new_group;
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MPI_Comm new_comm;
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MPI_Init(&argc,&argv);
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MPI_Comm_rank(MPI_COMM_WORLD, &rank);
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MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
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if (numtasks != NPROCS) {
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printf("Must specify MP_PROCS= %d. Terminating.\n",NPROCS);
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MPI_Finalize();
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}
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sendbuf = rank;
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/* Extract the original group handle */
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MPI_Comm_group(MPI_COMM_WORLD, &orig_group);
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/* Divide tasks into two distinct groups based upon rank */
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if (rank < NPROCS/2) {
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MPI_Group_incl(orig_group, NPROCS/2, ranks1, &new_group);
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}
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else {
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MPI_Group_incl(orig_group, NPROCS/2, ranks2, &new_group);
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}
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/* Create new new communicator and then perform collective communications */
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MPI_Comm_create(MPI_COMM_WORLD, new_group, &new_comm);
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MPI_Allreduce(&sendbuf, &recvbuf, 1, MPI_INT, MPI_SUM, new_comm);
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MPI_Group_rank (new_group, &new_rank);
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printf("rank= %d newrank= %d recvbuf= %d\n",rank,new_rank,recvbuf);
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MPI_Finalize();
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}
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