sc_reduce_tmpsum Subroutine

  subroutine sc_reduce_tmpsum(self)
    use mp, only: sum_allreduce_sub, sum_reduce_sub, nb_sum_reduce_sub
    implicit none
    class(supercell_type), intent(in out) :: self
    integer :: ic
    complex, dimension(self%nrow) :: local_tmp_sum

    ! Zero out the local tmp_sum
    local_tmp_sum = 0.0

    !NOTE: Here we rely on the cells having not reduced/
    !gathered their data yet so there are no repeated rows.
    ! Clearly cells%tmp_sum must be the same size as self%tmp_sum
    ! at this point. If cells only updated a subset of their tmp_sum
    ! entries we could perhaps save some work here by only summing over
    ! the set regions. Currently the work involved here does not scale
    ! at all with increasing processor count _beyond_ changes to cell
    ! locality (i.e. when is_empty triggers).
    !First do local sums
    !$OMP PARALLEL DO DEFAULT(none) &
    !$OMP PRIVATE(ic) &
    !$OMP SHARED(self) &
    !$OMP REDUCTION(+: local_tmp_sum) &
    !$OMP SCHEDULE(static)
    do ic = 1, self%ncell
       if (self%cells(ic)%is_empty) cycle
       local_tmp_sum = local_tmp_sum + self%cells(ic)%tmp_sum
    end do
    !$OMP END PARALLEL DO

    ! Copy local tmp_sum into super cell variant. Note this is an added cost
    ! due to OpenMP requiring us to use a non-member variable in reduction
    ! clauses. If this file was preprocessed then we could imagine offering
    ! an alternative code-path here for non-OpenMP builds.
    self%tmp_sum = local_tmp_sum

    !<DD>TAGGED: As we currently have to do fm_gather_fields on every time step we only need
    !to reduce to the head of the supercell, which may be an all_local proc in which case we don't
    !want to do any reduction. If it's a pd proc then really we should just do reduce_sub rather
    !than allreduce_sub as we're going to broadcast the result later anyway.
    !if(self%sc_sub_pd%nproc.gt.0) call sum_allreduce_sub(self%tmp_sum,self%sc_sub_pd%id)
    if (.not.(self%is_empty .or. self%is_all_local)) then
       !AJ If non-blocking collectives are enabled and available on the system then call them here
       if (field_local_nonblocking_collectives) then
          call nb_sum_reduce_sub(self%tmp_sum, 0, self%sc_sub_pd, self%collective_request)
       else
          call sum_reduce_sub(self%tmp_sum, 0, self%sc_sub_pd)
       end if
    end if
    !<DD> At this point the head of the supercell has the field update stored in self%tmp_sum
    !all other procs have partial/no data
  end subroutine sc_reduce_tmpsum