res Subroutine

   pure subroutine res(t, c, cdot, cj, delta, ires, rpar, ipar)
   !! This routine computes the residuals vector, using subroutine `f` for the right-hand
   !! sides.

      use web_par, only: ns, np, mx, my, mxns
   
      real(rk), intent(in) :: t
      real(rk), intent(in) :: c(*)
      real(rk), intent(in) :: cdot(*)
      real(rk), intent(in) :: cj
      real(rk), intent(out) :: delta(*)
      integer, intent(inout) :: ires
      real(rk), intent(inout) :: rpar(*)
      integer, intent(inout) :: ipar(*)

      integer :: i, ic0, ici, iyoff, jx, jy

      call f(t, c, delta, rpar)

      do jy = 1, my
         iyoff = mxns*(jy - 1)
         do jx = 1, mx
            ic0 = iyoff + ns*(jx - 1)
            do i = 1, ns
               ici = ic0 + i
               if (i > np) then
                  delta(ici) = -delta(ici)
               else
                  delta(ici) = cdot(ici) - delta(ici)
               end if
            end do
         end do
      end do

   end subroutine res