Splitting an array in OPENMPI and combining results [c/c++]

readme.md

compile

mpic++ -O0  -c main.c -o main.o

link

mpic++ -g main.o -o mpi_test

run

create the his file

hostname > hostfile

run the binary with mpirun

mpirun  --use-hwthread-cpus  -hostfile hostfile ./mpi_test

main.c

#include "stdio.h"
#include <stdlib.h>
#include <math.h>
#include <mpi.h>

int main(int argc, char *argv[])
{
    int process_Rank, size_Of_Comm;
    double distro_Array[] = {1, 2, 3, 4, 5, 6 ,7, 8, 9, 10, 11, 12, 13, 14}; // data to be distributed
    int N = sizeof(distro_Array)/sizeof(distro_Array[0]);
    
    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &size_Of_Comm);
    MPI_Comm_rank(MPI_COMM_WORLD, &process_Rank);

    double scattered_Data[2];
    int i;
    if(process_Rank==0)
    {
        for(i=1;i<size_Of_Comm;i++)
        {  
            if(2*i<=N)
            {
                printf("scattering data %f\n", *((distro_Array)+2*i));  
                MPI_Send(
                    distro_Array+2*(i-1),      //Address of the message we are sending.
                    2,                  //Number of elements handled by that address.
                    MPI_DOUBLE,            //MPI_TYPE of the message we are sending.
                    i,                  //Rank of receiving process
                    1,                  //Message Tag
                    MPI_COMM_WORLD      //MPI Communicator
                );
            }
        }
    }
    else
    {
        printf("waiting for data by %d\n", process_Rank);
        if(2*process_Rank<=N)
        {
            MPI_Recv(
                    &scattered_Data,      //Address of the message we are receiving.
                    2,                  //Number of elements handled by that address.
                    MPI_DOUBLE,            //MPI_TYPE of the message we are sending.
                    0,                  //Rank of sending process
                    1,                  //Message Tag
                    MPI_COMM_WORLD,      //MPI Communicator
                    MPI_STATUS_IGNORE   //MPI Status Object
                );
            printf("Process %d has received:  ",process_Rank);
            double sum=0;
            for(int i =0;i<2;i++)
            {
                printf("%f ", scattered_Data[i]);
                sum += scattered_Data[i];
            }
            MPI_Send(
                &sum,      //Address of the message we are sending.
                1,                  //Number of elements handled by that address.
                MPI_DOUBLE,            //MPI_TYPE of the message we are sending.
                0,                  //Rank of receiving process
                1,                  //Message Tag
                MPI_COMM_WORLD      //MPI Communicator
                );
            printf("\n");
        }
    }
    MPI_Barrier(MPI_COMM_WORLD); // all the sub ranks/processes waits here
   /* process 0 will aggregate the results*/
    if(process_Rank==0)
    {
        for(i=1;i<size_Of_Comm;i++)
        {
            double sum=0;
            MPI_Recv(
                    &sum,      //Address of the message we are receiving.
                    1,                  //Number of elements handled by that address.
                    MPI_DOUBLE,            //MPI_TYPE of the message we are sending.
                    i,                  //Rank of sending process
                    1,                  //Message Tag
                    MPI_COMM_WORLD,      //MPI Communicator
                    MPI_STATUS_IGNORE   //MPI Status Object
                );
            printf("Process %d has sent: %f \n", i, sum);
        }
    }
    MPI_Finalize();
    return 0;
}

openmpi , parallel, splitting , MPI_Recv , MPI_Barrier , MPI_Send