compute_flux2D Subroutine

  subroutine compute_flux2D(vm, flux_density, area, fraction, allsum, dstflux, rc)
    type(ESMF_VM), intent(in)        :: vm
    real(ESMF_KIND_R8), pointer      :: flux_density(:,:) 
    real(ESMF_KIND_R8), pointer      :: area(:,:) 
    real(ESMF_KIND_R8), pointer      :: fraction(:,:) 
    real(ESMF_KIND_R8), intent(out)  :: allsum(3)
    logical, intent(in) , optional   :: dstflux
    integer, intent(out), optional   :: rc

    real(ESMF_KIND_R8)               :: sum(3)
    integer                          :: i,j, localrc, npet, lpet
    logical                          :: l_dstflux

    if(present(rc)) rc = ESMF_SUCCESS
    l_dstflux = .false.
    if(present(dstflux)) l_dstflux = dstflux

    call ESMF_VMGet(vm, petCount=npet, localPet=lpet, rc=localrc)
    if (ESMF_LogFoundError(localrc, &
        ESMF_ERR_PASSTHRU, &
        ESMF_CONTEXT, rcToReturn=rc)) return
  
    !if(lpet == 0) write(*, '(A, 4I5)') 'compute_flux2D bounds: ', &
    !  lbound(flux_density, 1), ubound(flux_density, 1), &
    !  lbound(flux_density, 2), ubound(flux_density, 2)

    sum = 0.
    do i = lbound(flux_density, 1), ubound(flux_density, 1)
      do j = lbound(flux_density, 2), ubound(flux_density, 2)
        if(l_dstflux) then
          sum(1) = sum(1) + flux_density(i,j)*area(i,j)
        else
          sum(1) = sum(1) + flux_density(i,j)*area(i,j)*fraction(i,j)
        endif
        sum(2) = sum(2) +                 area(i,j)*fraction(i,j)
        sum(3) = sum(3) +                 area(i,j)
      enddo
    enddo

    call ESMF_VMAllReduce(vm, sum, allsum, 3, ESMF_REDUCE_SUM, rc=localrc)
    if (ESMF_LogFoundError(localrc, &
        ESMF_ERR_PASSTHRU, &
        ESMF_CONTEXT, rcToReturn=rc)) return

  end subroutine compute_flux2D