subroutine MPP_SUM_( a, length, pelist )
!sums array a over the PEs in pelist (all PEs if this argument is omitted)
!result is also automatically broadcast: all PEs have the sum in a at the end
!we are using f77-style call: array passed by address and not descriptor; further, the f90 conformance check is avoided.
      integer, intent(in) :: length
      integer, intent(in), optional :: pelist(:)
      MPP_TYPE_, intent(inout) :: a(*)

      if( .NOT.module_is_initialized )call mpp_error( FATAL, 'MPP_SUM: You must first call mpp_init.' )
      return
    end subroutine MPP_SUM_

!#######################################################################
#include <mpp_sum.inc>