flow_exchange_cell_matrix Subroutine

   subroutine flow_exchange_cell_matrix(flow, field)
      use mod_profiling, only : profiler_start, profiler_stop
      type(flow_mpi_t), intent(inout) :: flow
      real(rk), intent(inout) :: field(:,:)
      integer, parameter :: cell_matrix_halo_tag = 9282
      integer :: ncomp, i, j, k, nreq, ierr, offset, count, pos

      if (.not. allocated(flow%cell_sendbuf)) return
      if (flow%ncell_recv_ranks + flow%ncell_send_ranks == 0) return

      ncomp = size(field, 1)
      if (ncomp > flow%cell_halo_max_components) then
         call fatal_error('mpi_flow', 'cell matrix halo component count exceeds cached buffer size')
      end if

      do i = 1, flow%ncell_send_ranks
         offset = flow%cell_send_displs(i)
         count = flow%cell_send_counts(i)
         do j = 1, count
            pos = (offset + j - 1) * ncomp
            do k = 1, ncomp
               flow%cell_sendbuf(pos + k) = field(k, flow%cell_send_cells(offset + j))
            end do
         end do
      end do

      call profiler_start('MPI_Communication')
      nreq = 0
      do i = 1, flow%ncell_recv_ranks
         offset = flow%cell_recv_displs(i) * ncomp
         count = flow%cell_recv_counts(i) * ncomp
         nreq = nreq + 1
         call MPI_Irecv(flow%cell_recvbuf(offset + 1), count, MPI_DOUBLE_PRECISION, &
                        flow%cell_recv_ranks(i), cell_matrix_halo_tag, flow%comm, flow%cell_requests(nreq), ierr)
         call check_mpi(ierr, 'cell matrix halo irecv')
      end do
      do i = 1, flow%ncell_send_ranks
         offset = flow%cell_send_displs(i) * ncomp
         count = flow%cell_send_counts(i) * ncomp
         nreq = nreq + 1
         call MPI_Isend(flow%cell_sendbuf(offset + 1), count, MPI_DOUBLE_PRECISION, &
                        flow%cell_send_ranks(i), cell_matrix_halo_tag, flow%comm, flow%cell_requests(nreq), ierr)
         call check_mpi(ierr, 'cell matrix halo isend')
      end do
      call MPI_Waitall(nreq, flow%cell_requests(1:nreq), MPI_STATUSES_IGNORE, ierr)
      call check_mpi(ierr, 'cell matrix halo waitall')
      call profiler_stop('MPI_Communication')

      do i = 1, size(flow%cell_recv_cells)
         pos = (i - 1) * ncomp
         do k = 1, ncomp
            field(k, flow%cell_recv_cells(i)) = flow%cell_recvbuf(pos + k)
         end do
      end do
   end subroutine flow_exchange_cell_matrix