rt Subroutine

   pure subroutine rt(neq, t, y, yprime, nrt, rval, rpar, ipar)
     !! Roots routine.
      integer, intent(in) :: neq
      real(rk), intent(in) :: t
      real(rk), intent(in) :: y(neq)
      real(rk), intent(in) :: yprime(neq)
      integer, intent(in) :: nrt
      real(rk), intent(out) :: rval(nrt)
      real(rk), intent(in) :: rpar
      integer, intent(in) :: ipar

      rval(1) = y(1)

   end subroutine rt