#include <iostream>
#include <vector>
#include "mpi.h"
using namespace std;

int main( int argc, char* argv[] )
{
   int rank, nproc;
   MPI_Status stat;

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

   int tag = 1;
   if ( rank == 0 )                                   // Root processor (0)
   {
      vector<double> A = { 10, 20, 30, 40, 50 };                           // Some data
      int n = A.size();
      MPI_Send( &n, 1, MPI_INT, 1, tag, MPI_COMM_WORLD );                  // Send size
      MPI_Send( A.data(), n, MPI_DOUBLE, 1, tag, MPI_COMM_WORLD );         // Send data
   }
   else if ( rank == 1 )                              // Next processor (1)
   {
      int n;
      MPI_Recv( &n, 1, MPI_INT, 0, tag, MPI_COMM_WORLD, &stat );           // Receive size
      vector<double> B(n);                                                 // Allocate buffer
      MPI_Recv( B.data(), n, MPI_DOUBLE, 0, tag, MPI_COMM_WORLD, &stat );  // Receive data

      cout << "Processor " << rank << " received " << n << " pieces of data: ";
      for ( double x : B ) cout << x << " ";
      cout << '\n';
   }
   MPI_Finalize();
}