#include <stdio.h>
#include <stdlib.h>
#include "mpi.h"

#define NUMBER_OF_TESTS 10

/*
 * This is similar to barrier, except it times a SINGLE allreduce on a 
 * double.
 */

int main( argc, argv )
int argc;
char **argv;
{
    int          rank;
    int          size;
    double       t1, t2, tmin;
    double       d_in, d_out;
    int          j, k, nloop;

    MPI_Init( &argc, &argv );

    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    if (rank == 0 && size == 1) 
	printf( "Kind\t\tnp\ttime (sec)\n" );

    nloop = 1000;
    tmin  = 1000;
    for (k=0; k<NUMBER_OF_TESTS; k++) {
	MPI_Barrier( MPI_COMM_WORLD );
	d_in = 1.0;
	t1 = MPI_Wtime();
	for (j=0; j<nloop; j++) {
	    MPI_Allreduce( &d_in, &d_out, 1, MPI_DOUBLE, MPI_SUM, 
			   MPI_COMM_WORLD );
	}
	t2 = (MPI_Wtime() - t1) / nloop;
	if (t2 < tmin) tmin = t2;
    }

    if (rank == 0) {
	printf( "Allreduce\t%d\t%f\n", size, tmin );
    }

    MPI_Finalize( );
    return 0;
}