mpi_collective_scatterv.cpp

# include <iostream>
# include <cstdlib> // has exit(), etc.
# include <ctime>
# include <stdio.h>
# include "mpi.h"   // MPI header file

#define SIZE 4
using namespace std;

int main (int argc, char **argv)
{
	int nprocs, rank;

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

	// the data to be distributed
	char data[SIZE][SIZE] = {
		{'a', 'b', 'c', 'd'},
		{'e', 'f', 'g', 'h'},
		{'i', 'j', 'k', 'l'},
		{'m', 'n', 'o', 'p'}
	};

	char rec_buf[100];
	int sendcounts[nprocs];
	int displs[nprocs];

	// calculate send counts and displacements
	// Your code

	for (int i = 0; i < nprocs; i++) 
	{
		sendcounts[i] = i+1;
		displs[i] = i*nprocs;
	} 

	// print calculated send counts and displacements for each process
	if (rank == 0) {
		for (int i = 0; i < nprocs; i++) {
			printf("sendcounts[%d] = %d\tdispls[%d] = %d\n", i, sendcounts[i], i, displs[i]);
		}
	}

	// MPI_Scatterv
	// Your code
	
	MPI_Scatterv(&data, sendcounts, displs, MPI_CHAR, &rec_buf, 100, MPI_CHAR, 0, MPI_COMM_WORLD);

	printf("%d: ", rank);
	for (int i = 0; i < sendcounts[rank]; i++) {
		printf("%c\t", rec_buf[i]);
	}
	printf("\n");

	MPI_Finalize();
	return 0;
}