imk_residual Subroutine

  subroutine imk_residual(this, lev, dt, flags)
    class(pf_imk_t),   intent(inout) :: this
    class(pf_level_t), intent(inout) :: lev
    real(pfdp),        intent(in   ) :: dt
    integer, optional,   intent(in)    :: flags
    integer :: m

    call lev%ulevel%sweeper%integrate(lev, lev%Q, lev%F, dt, lev%I)

    ! add tau (which is 'node to node')
    if (allocated(lev%tauQ)) then
       do m = 1, lev%nnodes-1
          call lev%I(m)%axpy(1.0_pfdp, lev%tauQ(m))
       end do
    end if

    ! subtract out Q  (not initial condition is zero
    do m = 1, lev%nnodes-1
       call lev%R(m)%copy(lev%I(m))
       call lev%R(m)%axpy(-1.0_pfdp, lev%Q(m+1))
    end do

  end subroutine imk_residual