MPI_Allreduce

#include <stdio.h>
#include "mpi.h"
#include <malloc.h>

int main(int argc, char ** argv){
    int rank,size,rbuf[3],sbuf[3],i;
    MPI_Comm comm = MPI_COMM_WORLD;
    MPI_Status status;
    MPI_Init(&argc,&argv);
    MPI_Comm_size(comm, &size);
    MPI_Comm_rank(comm, &rank);
    printf("Process %d has:",rank);
    for(i = 0;i< 3;i++){
        sbuf[i] = rank*10 + i;
        printf(" %d",sbuf[i]);
    }
    putchar('\n');
    MPI_Allreduce(sbuf,rbuf,3,MPI_INT,MPI_SUM,comm);
    printf("process %d :total sum =:",rank);
    for(i = 0;i< 3;i++)
        printf(" %d",rbuf[i]);
    putchar('\n');
    MPI_Finalize();
    return 0;
}