! arrayMPIF.c
! Run this with 2 processors.  Processor 1 creates an array of 'count' random
! numbers.  In this example 'count' is 100.  Processor 0 (the root process)
! receives this array from processor 1.

! Make sure you are understanding what each parameter in the MPI calls represent.

        program main
        include "mpif.h"

        integer MAXVALS, NUMSPERLINE
        parameter (MAXVALS=100,NUMSPERLINE=10)
        integer rank, size, count, data(MAXVALS)
        real randomarray(5)
        integer ierr, status(MPI_STATUS_SIZE)

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

        call random_seed()
        call random_seed()
        count = 100

        if (rank .eq. 0) then
                call MPI_RECV(data, 100, MPI_DOUBLE, 1, 10, &
                        MPI_COMM_WORLD, status, ierr);
                print *, 'Data received from process 1:'
!  THIS DO LOOP PRINTS ONE ARRAY ELEMENT PER LINE
!               do i = 1, count
!                       print *, data(i)
!               end do

! THIS VERSION USES AN 'IMPLIED DO LOOP' IN THE WRITE STATEMENT TO PRINT
! 10 NUMBERS PER LINE. LET ME KNOW IF YOU FIND AN EASIER WAY TO DO THIS.

               do i = 1, count/NUMSPERLINE  ! Make count divisible by NUMSPERLINE
                        write(*,"(10I7)") &
                   (data(j), j=(i-1)*NUMSPERLINE+1, (i-1)*NUMSPERLINE+NUMSPERLINE)
                end do
        else
                if (rank .eq. 1) then
                        do i = 1, count
                                call random_number(randomarray)
                                data(i) = int(randomarray(1)*1000)
                        end do
                        call MPI_SEND(data, count, MPI_DOUBLE, 0, 10, &
                                MPI_COMM_WORLD, ierr);
                end if
        end if

        call MPI_FINALIZE();

        end program

! CRAY SV1:

! f90 arrayMPIF.f90

! mpirun -np 2 a.out

! Data received from process 1:
!    950    275    831     83    212     18    584    871    464    763
!    210    926     93    183    722    422    576    589    804    702
!    485    854    184    812    362    764    916    957    911    542
!     47    529    185    955    589    190    850    180      3    104
!     66    404    557    937    447    954     34    205     60    316
!    827    778    415    653    906    392    331    939    258    522
!    635    366    154    324    871    765    997    134    952     39
!    951    489    473    383    516    166    972    919    269    620
!    568    508    191    507    378    341    192    997    948    523
!     18    234    372    587     32    688    153    625     23    136