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#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#define NTASKS 4
void print_buffers(int *printbuffer, int *sendbuffer, int buffersize);
void init_buffers(int *sendbuffer, int *recvbuffer, int buffersize);
int main(int argc, char *argv[])
{
int ntasks, rank, color;
int sendbuf[2 * NTASKS], recvbuf[2 * NTASKS];
int printbuf[2 * NTASKS * NTASKS];
MPI_Comm sub_comm;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (ntasks != NTASKS) {
if (rank == 0) {
fprintf(stderr, "Run this program with %i tasks.\n", NTASKS);
}
MPI_Abort(MPI_COMM_WORLD, -1);
}
/* Initialize message buffers */
init_buffers(sendbuf, recvbuf, 2 * NTASKS);
/* Print data that will be sent */
print_buffers(printbuf, sendbuf, 2 * NTASKS);
/* Send (0,1,2,...,7) everywhere */
MPI_Bcast(sendbuf, 2 * NTASKS, MPI_INT, 0, MPI_COMM_WORLD);
/* Print data that was received */
print_buffers(printbuf, sendbuf, 2 * NTASKS);
MPI_Finalize();
return 0;
}
void init_buffers(int *sendbuffer, int *recvbuffer, int buffersize)
{
int rank, i;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
for (i = 0; i < buffersize; i++) {
recvbuffer[i] = -1;
sendbuffer[i] = i + buffersize * rank;
}
}
void print_buffers(int *printbuffer, int *sendbuffer, int buffersize)
{
int i, j, rank, ntasks;
MPI_Gather(sendbuffer, buffersize, MPI_INT,
printbuffer, buffersize, MPI_INT, 0, MPI_COMM_WORLD);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
if (rank == 0) {
for (j = 0; j < ntasks; j++) {
printf("Task %i:", j);
for (i = 0; i < buffersize; i++) {
printf(" %2i", printbuffer[i + buffersize * j]);
}
printf("\n");
}
printf("\n");
}
}