Intel® MPI Library Developer Guide for Linux* OS

ID 768728
Date 12/16/2022

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#include <mpi.h>
#include <omp.h>
#define n 2
MPI_Comm split_comm[n];
int main()
    int i, provided;
    MPI_Init_thread(NULL, NULL, MPI_THREAD_MULTIPLE, &provided);
    for (i = 0; i < n; i++)
        MPI_Comm_dup(MPI_COMM_WORLD, &split_comm[i]);
#pragma omp parallel for num_threads(n)
    for (i = 0; i < n; i++) {
        int j = i;
        MPI_Allreduce(MPI_IN_PLACE, &j, 1, MPI_INT, MPI_SUM, split_comm[i]);
        printf("Thread %d: allreduce returned %d\n", i, j);