collectivecomm.c

#include "mpi.h"
#include <stdio.h>
#define SIZE 4

int main(int argc, char *argv[])  {
int numtasks, rank, sendcount, recvcount, source;
float sendbuf[SIZE][SIZE] = {
    {1.0, 2.0, 3.0, 4.0},
    {5.0, 6.0, 7.0, 8.0},
    {9.0, 10.0, 11.0, 12.0},
    {13.0, 14.0, 15.0, 16.0}  };
float recvbuf[SIZE];

MPI_Init(&argc,&argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &numtasks);

if (numtasks == SIZE) {
    // define source task and elements to send/receive, then perform collective scatter
    source = 1;
    sendcount = SIZE;
    recvcount = SIZE;
    MPI_Scatter(sendbuf,sendcount,MPI_FLOAT,recvbuf,recvcount,
                MPI_FLOAT,source,MPI_COMM_WORLD);

    printf("rank= %d  Results: %f %f %f %f\n",rank,recvbuf[0],
        recvbuf[1],recvbuf[2],recvbuf[3]);
    }
else
    printf("Must specify %d processors. Terminating.\n",SIZE);

MPI_Finalize();
return 0;
}