mpi_collective_scatter.cpp

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

using namespace std;

//****************************************************************************80
int main (int argc, char **argv)
	//****************************************************************************80
{
	int data_array[8] = {0};
	int recv_buffer[1] = {0};
	int nprocs, rank;

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

	if (rank == 0) {	// root
		for (int i=0; i<8; i++) {
			data_array[i] = 100+i;
		}
	}

	int send_count = 2;
	int recv_count = 2;

	cout << "Before Scatter, data_array = ";
	for (int j=0; j<8; j++) {cout << data_array[j] << " ";}
	cout << " in rank = " << rank << endl;
	cout << "Before Scatter, recv_buffer = ";
	for (int j=0; j<1; j++) {cout << recv_buffer[j] << " ";}
	cout << " in rank = " << rank << endl;

	
	MPI_Scatter(&data_array, send_count, MPI_INT, &recv_buffer, recv_count, MPI_INT, 0, MPI_COMM_WORLD);
	

	cout << "After Scatter, data_array = ";
	for (int j=0; j<8; j++) {cout << data_array[j] << " ";}
	cout << " in rank = " << rank << endl;
	cout << "After Scatter, recv_buffer = ";
	for (int j=0; j<1; j++) {cout << recv_buffer[j] << " ";}
	cout << " in rank = " << rank << endl;

	MPI_Finalize();
	return 0;
}