[OMPI users] Doubt regarding MPI_GATHER

[Arunkumar C R]

Hello,

I have written an MPI code to find acceleration (a = F/m) of a system of
particles. I would like to know how to perform MPI_GATHER of all the output
data at the root process and print the whole array (in the present case,
f(1:n) ) and reuse it  for some other purpose in the serial part of the same
code.  Please check the program given below and give me a solution.

program g
        use mpi
        implicit none

        real(kind(1d0)),allocatable,dimension(:)::a, f
        real(kind(1d0))::m
        integer::i, n, true, ierr, np, irank, istart, iend, var, nprocs

        nprocs= 4                !no: of processors used
        n = 100                  !no: of array elements
        m = 12.0d0               !mass of the moving particle
        var = n / nprocs         !no: of array elements per process
        allocate(a(n), f(n), stat=true)
        if(true.ne.0)  print*,'mem err'

        call mpi_init(ierr)
        call mpi_comm_size(mpi_comm_world,    np, ierr)
        call mpi_comm_rank(mpi_comm_world, irank, ierr)
        istart= irank * var + 1
        iend  = (irank + 1) * var

        do i= istart, iend
                f(i) = dble(i)           !the magnitude of force is taken
as  continuous (real) numbers !!
                a(i) = f(i) / m
        end do
        if(irank.eq.0) then          !root process
            do i=1,n
                print*,i,a(i)              !here, all the root elements are
printed correctly and the other elements as zeroes
            end do
        end if
  call mpi_finalize(ierr)
end


Thanks in Advance
arun