Hello World programs

Hello world example code for debugging and testing.

MPI hello world:

program hello_world
use mpi

integer :: rank, comm_size, ierr, tag, status(MPI_STATUS_SIZE)

call mpi_init(ierr)
call mpi_comm_size(mpi_comm_world, comm_size, ierr)
call mpi_comm_rank(mpi_comm_world, rank, ierr)

print*, 'Hello from rank ', rank, ' of ', comm_size
call mpi_finalize(ierr)

end program 

MPI hello world to test f77 vs f08 mpi bindings (this is a problem for DART with mpich 4 https://github.com/NCAR/DART/issues/261).

The issue has a mpi_f08 version. 

Run with 2 processors:

program hello_world

use mpi

implicit none

integer :: rank, nprocs, ierr
integer :: tag, count
integer :: status(MPI_STATUS_SIZE)
real :: a, b
integer :: a_int, b_int

count = 1 
tag = 1
a = 10.13
b = 4.34
a_int = 77
b_int = 3

call mpi_init(ierr)
call mpi_comm_size(MPI_COMM_WORLD, nprocs, ierr)
call mpi_comm_rank(MPI_COMM_WORLD, rank, ierr)

if (rank .eq. 0) then
  call mpi_send(a, count, MPI_REAL, 1, tag, MPI_COMM_WORLD, ierr)
else
  call mpi_recv(b, count,  MPI_REAL, 0, tag, MPI_COMM_WORLD, status, ierr)
endif

if (rank .eq. 0) then
  call mpi_send(a_int, count, MPI_INTEGER, 1, tag, MPI_COMM_WORLD, ierr)
else
  call mpi_recv(b_int, count,  MPI_INTEGER, 0, tag, MPI_COMM_WORLD, status, ierr)
endif

print*, 'Hello world from process: ', rank, 'of', nprocs

call mpi_finalize(ierr)

end program