/*
 * Test the connectivity between all processes.
 */

#pragma ident "@(#)connectivity.c 1.1 99/02/02"

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <unistd.h>

#include <mpi.h>

int
main(int argc, char **argv)
{
    MPI_Status  status;
    int         verbose = 0;
    int         rank;
    int         np;	                 /* number of processes in job
*/
    int         peer;
    int         i;
    int         j;

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

    if (argc>1 && strcmp(argv[1], "-v")==0)
        verbose = 1;

    for (i=0; i<np; i++) {
        if (rank==i) {
            /* rank i sends to and receives from each higher rank
*/
            for(j=i+1; j<np; j++) {
                if (verbose)
                  printf("checking connection %4d <->
%-4d\n", i, j);
                MPI_Send(&rank, 1, MPI_INT, j, rank, MPI_COMM_WORLD);
               MPI_Recv(&peer, 1, MPI_INT, j, j, MPI_COMM_WORLD, &status);
            }
        } else if (rank>i) {
            /* receive from and reply to rank i */
          MPI_Recv(&peer, 1, MPI_INT, i, i, MPI_COMM_WORLD, &status);
            MPI_Send(&rank, 1, MPI_INT, i, rank, MPI_COMM_WORLD);
        }
    }

    MPI_Barrier(MPI_COMM_WORLD);
    if (rank==0)
        printf("Connectivity test on %d processes PASSED.\n", np);

    MPI_Finalize();
    return 0;
}

!
! Estimate pi via Monte-Carlo method.
! 
! Each process sums how many of samplesize random points generated 
! in the square (-1,-1),(-1,1),(1,1),(1,-1)
fall in the circle of 
! radius 1 and center (0,0), and then estimates pi from the formula
! pi = (4 * sum) / samplesize.
! The final estimate of pi is calculated at rank 0 as the average
of 
! all the estimates.
!
        program monte

        include 'mpif.h'

        double precision drand
        external drand

        double precision x, y, pi, pisum
        integer*4 ierr, rank, np
        integer*4 incircle, samplesize

        parameter(samplesize=2000000)

        call MPI_INIT(ierr)
        call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
        call MPI_COMM_SIZE(MPI_COMM_WORLD, np, ierr)

!       seed random number generator
        x = drand(2 + 11*rank)

        incircle = 0
        do i = 1, samplesize
           x = drand(0)*2.0d0 - 1.0d0     ! generate a
random point
           y = drand(0)*2.0d0 - 1.0d0

           if ((x*x + y*y) .lt. 1.0d0) then
              incircle = incircle+1       ! point is in the circle
           endif
        end do

        pi = 4.0d0 * DBLE(incircle) / DBLE(samplesize)

!       sum estimates at rank 0
         call MPI_REDUCE(pi, pisum, 1, MPI_DOUBLE_PRECISION, MPI_SUM, 
      &         0 , MPI_COMM_WORLD, ierr)

        if (rank .eq. 0) then
!          final estimate is the average
           pi = pisum / DBLE(np)
              print '(A,I4,A,F8.6,A)','Monte-Carlo estimate
of pi by ',np,
      &          ' processes is ',pi,'.'
        endif

        call MPI_FINALIZE(ierr)
        end