High-Performance Design Patterns for Modern Fortran

Listing 11

subroutine mpi_begin

integer:: dims(), periods(), reorder

! prevent accidentally starting MPI

! if it has already been initiated

 if (program_status .eq. 0) then

 call MPI_INIT(ierr)

 call MPI_COMM_SIZE(MPI_COMM_WORLD, num_procs, ierr)

 call MPI_COMM_RANK(MPI_COMM_WORLD, my_id, ierr)

 ! Create a 1D Cartesian partition

 ! with reordering and periodicity

 dims = num_procs

 reorder = .true.

 periods = .true.

 call MPI_CART_CREATE(MPI_COMM_WORLD, 1, dims, periods, reorder, MPI_COMM_CART, ierr)

 call MPI_COMM_RANK(MPI_COMM_CART, my_id, ierr)

 call MPI_CART_SHIFT(MPI_COMM_CART, 0, 1, left_id, right_id, ierr)

 program_status = 1

  endif

end subroutine