sc_pull_rows_to_arr Subroutine

  subroutine sc_pull_rows_to_arr(self,arr)
    !AJ Nonblocking?
    use mp, only: sum_allreduce_sub
    implicit none
    class(supercell_type), intent(in) :: self
    complex, dimension(:,:), intent(out) :: arr !Note: Dimensions should be self%ncol, self%nrow
    integer :: ic, rl,ru, cl,cu, irb

    ! Zero out arr |--> Not needed if gathering
    ! This may look like it is only needed for the sum_allreduce_sub branch below,
    ! however without this line we would end up not setting arr in cases where we
    ! think of this supercell as empty. This is usually fine, but for the ky=kx=0
    ! mode all processors consider the supercell to be empty, but we still need to
    ! initialise this array in some cases (e.g. when dumping to file). We could
    ! attempt to only do this zeroing in this special case to save some time, but
    ! we don't expect to be calling this routine much so opt for simpler approach.
    arr=0
    
    !Now see if we want to exit
    if(self%is_empty) return
    if(.not.self%is_local) return

    !If we're all local then just do things simply as we don't need comms
    if(self%is_all_local) then
       do ic=1,self%ncell
          do irb=1,self%cells(ic)%nrb
             rl=self%cells(ic)%rb(irb)%row_llim
             ru=self%cells(ic)%rb(irb)%row_ulim
             cl=self%cells(ic)%rb(irb)%col_llim
             cu=self%cells(ic)%rb(irb)%col_ulim
             arr(cl:cu,rl:ru)=self%cells(ic)%rb(irb)%data
          enddo
       enddo
    else

       !Place local piece in arr
       do ic=1,self%ncell
          if(self%cells(ic)%is_empty) cycle
          do irb=1,self%cells(ic)%nrb
             rl=self%cells(ic)%rb(irb)%row_llim
             ru=self%cells(ic)%rb(irb)%row_ulim
             cl=self%cells(ic)%rb(irb)%col_llim
             cu=self%cells(ic)%rb(irb)%col_ulim
             arr(cl:cu,rl:ru)=self%cells(ic)%rb(irb)%data
          enddo
       enddo

       !Now use MPI to get the rest of the data from other procs
       !<DD>FOR NOW USE ALL_REDUCE AS EASIER, BUT SHOULD BE ABLE
       !TO DO THIS WITH ALL_GATHERV WHICH SHOULD BE FASTER
       if(self%sc_sub_pd%nproc.gt.0) call sum_allreduce_sub(arr,self%sc_sub_pd%id)
    endif

  end subroutine sc_pull_rows_to_arr