box_clpl Subroutine

  subroutine box_clpl(mg, id, nc, i_out)
    type(mg_t), intent(inout) :: mg
    integer, intent(in)       :: id
    integer, intent(in)       :: nc
    integer, intent(in)       :: i_out
    !< Index of variable to store Laplacian in
    integer                   :: i, j
    real(dp)                  :: dr(2), idr2(2)
    real(dp)                  :: r_face(nc+1), r_inv(nc)

    dr     = mg%dr(:, mg%boxes(id)%lvl)
    idr2   = 1 / dr**2
    r_face = mg%boxes(id)%r_min(1) + dr(1) * [(i, i=0,nc)]
    r_inv  = 1/(mg%boxes(id)%r_min(1) + dr(1) * [(i-0.5_dp, i=1,nc)])

    associate (cc => mg%boxes(id)%cc, n => mg_iphi)
      do j = 1, nc
         do i = 1, nc
            cc(i, j, i_out) = idr2(1) * (r_face(i) * r_inv(i) * cc(i-1, j,&
                n) + r_face(i+1) * r_inv(i) * cc(i+1, j, n) - 2 * cc(i, j,&
                n)) + idr2(2) * (cc(i, j-1, n) +  cc(i, j+1, n) - 2 * cc(i, j,&
                n))
         end do
      end do
    end associate
  end subroutine box_clpl