// BasicMPI.cpp
// NKU CSC 333/601 - Fall 2002 - Kirby
// ------------------------------------------------------------
// A little program to demonstrate basic MPI in C++.
// Sends random vectors around the network, circularly.
//
/**************************************************************
Make sure your .rhosts file includes the lines:
    head.bobb.hpc.nku.edu yourusername
    b1.bobb.hpc.nku.edu   yourusername
    b2.bobb.hpc.nku.edu   yourusername
    b3.bobb.hpc.nku.edu   yourusername
    b4.bobb.hpc.nku.edu   yourusername
    b5.bobb.hpc.nku.edu   yourusername
    b6.bobb.hpc.nku.edu   yourusername
    b7.bobb.hpc.nku.edu   yourusername
    b8.bobb.hpc.nku.edu   yourusername
    b9.bobb.hpc.nku.edu   yourusername
    b10.bobb.hpc.nku.edu  yourusername
    b11.bobb.hpc.nku.edu  yourusername

NOTE: 
Contrary to earlier reports, there are only nodes 0-11, no node 12!

Before running, turn on MPI (the -v option confirms which nodes are up)
   lamboot -v lamhosts

To compile:
   mpiCC BasicMPI.cpp

To run on 12 nodes:
   mpirun -np 12 a.out
/***************************************************************/



#include <iostream>
#include <vector>
#include <fstream>
#include <algorithm>
#include <cstdlib>
#include <ctime>
using namespace std ;

#include "mpi.h" // a dummy version provided on CSC 333 web page



int main( int argc, char** argv ) 
{
    // In this example, all messages bear the same tag.
    const int TAG= 99 ;                      

    // Turn on MPI.
    MPI_Init( &argc, &argv ) ;   

    // How many processors are out there?
    int size ; 
    MPI_Comm_size( MPI_COMM_WORLD, &size ) ;  

    // Which processor am I? (0...size-1)
    int rank ;
    MPI_Comm_rank( MPI_COMM_WORLD, &rank ) ;  
    
    // Set the random number seed differently on each processor.
    srand( time(0) * (1+rank) ) ; 

    // Create a vector.
    vector<int> v(8) ;

    // Fill the vector with some (partially random) integers.
    for ( int i=0 ; i < v.size() ; ++i )
        v[i]= 1000*rank  +  rand()%100 ;

    // Sort the vector.
    std::sort( v.begin(), v.end() ) ;

    // Send my v to my "right" neighbor.
    int iDest= (rank+1) % size ;
    MPI_Send( &(v[0]), v.size(), MPI_INT, iDest, TAG, MPI_COMM_WORLD ) ;

    // Receive my "left" neighbor's message data into my v.
    int iSource= (rank-1+size) % size ;  // = (rank-1) mod size
    MPI_Status status ;
    MPI_Recv( &(v[0]), v.size(), MPI_INT, iSource, TAG, MPI_COMM_WORLD, &status ) ;

    // Have the head node write v to a file.
    if ( rank == 0 )
    {
        ofstream summary( "summary.txt" ) ;
        for ( int i=0 ; i < v.size() ; ++i )
            summary << v[i] << " " ;
        summary << endl << "That's all folks." << endl ;
        cout << "Wrote file summary.txt" << endl ;
    }

    // All done.
    MPI_Finalize() ; 
	return 0 ;
}