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               &      rn_wdmin1 + rn_wdmin2
            ll_tmp2 = ( ABS(   ssh(ji,jj,Kmm) -   ssh(ji+1,jj,Kmm) ) > 1.E-12 ) .AND.                   &
               &      ( MAX(   ssh(ji,jj,Kmm) ,   ssh(ji+1,jj,Kmm) ) >                                  &
               &        MAX( -ht_0(ji,jj)     , -ht_0(ji+1,jj)     ) + rn_wdmin1 + rn_wdmin2 )

            IF(ll_tmp1) THEN
               zcpx(ji,jj) = 1.0_wp
            ELSE IF(ll_tmp2) THEN
               ! no worries about  ssh(ji+1,jj,Kmm) -  ssh(ji  ,jj,Kmm) = 0, it won't happen ! here
               zcpx(ji,jj) = ABS( (ssh(ji+1,jj,Kmm) + ht_0(ji+1,jj) - ssh(ji,jj,Kmm) - ht_0(ji,jj)) &
                           &    / (ssh(ji+1,jj,Kmm) -  ssh(ji  ,jj,Kmm)) )
               zcpx(ji,jj) = MAX(MIN( zcpx(ji,jj) , 1.0_wp),0.0_wp)
            ELSE
               zcpx(ji,jj) = 0._wp
            END IF

            ll_tmp1 = MIN(   ssh(ji,jj,Kmm)              ,   ssh(ji,jj+1,Kmm)                 ) >       &
               &      MAX( -ht_0(ji,jj)                  , -ht_0(ji,jj+1)                     ) .AND.   &
               &      MAX(   ssh(ji,jj,Kmm) + ht_0(ji,jj),   ssh(ji,jj+1,Kmm) + ht_0(ji,jj+1) ) >       &
               &      rn_wdmin1 + rn_wdmin2
            ll_tmp2 = ( ABS(   ssh(ji,jj,Kmm) -   ssh(ji,jj+1,Kmm) ) > 1.E-12 ) .AND.                   &
               &      ( MAX(   ssh(ji,jj,Kmm) ,   ssh(ji,jj+1,Kmm) ) >                                  &
               &        MAX( -ht_0(ji,jj)     , -ht_0(ji,jj+1)     ) + rn_wdmin1 + rn_wdmin2 )

            IF(ll_tmp1) THEN
               zcpy(ji,jj) = 1.0_wp
            ELSE IF(ll_tmp2) THEN
               ! no worries about  ssh(ji,jj+1,Kmm) -  ssh(ji,jj  ,Kmm) = 0, it won't happen ! here
               zcpy(ji,jj) = ABS( (ssh(ji,jj+1,Kmm) + ht_0(ji,jj+1) - ssh(ji,jj,Kmm) - ht_0(ji,jj)) &
                           &    / (ssh(ji,jj+1,Kmm) -  ssh(ji,jj  ,Kmm)) )
               zcpy(ji,jj) = MAX(MIN( zcpy(ji,jj) , 1.0_wp),0.0_wp)
            ELSE
               zcpy(ji,jj) = 0._wp
            ENDIF
         END_2D
      ENDIF

      ! Clean 3-D work arrays
      zhpi(:,:,:) = 0._wp
      zrhh(:,:,:) = rhd(A2D(nn_hls),:)

      ! Preparing vertical density profile "zrhh(:,:,:)" for hybrid-sco coordinate
      DO_2D( 1, 1, 1, 1 )
         jk = mbkt(ji,jj)
         IF(     jk <=  1   ) THEN   ;   zrhh(ji,jj,    :   ) = 0._wp
         ELSEIF( jk ==  2   ) THEN   ;   zrhh(ji,jj,jk+1:jpk) = rhd(ji,jj,jk)
         ELSEIF( jk < jpkm1 ) THEN
            DO jkk = jk+1, jpk
               zrhh(ji,jj,jkk) = interp1(gde3w(ji,jj,jkk  ), gde3w(ji,jj,jkk-1),   &
                  &                      gde3w(ji,jj,jkk-2), zrhh (ji,jj,jkk-1), zrhh(ji,jj,jkk-2))
            END DO
         ENDIF
      END_2D

      ! Transfer the depth of "T(:,:,:)" to vertical coordinate "zdept(:,:,:)"
      DO_2D( 1, 1, 1, 1 )
         zdept(ji,jj,1) = 0.5_wp * e3w(ji,jj,1,Kmm) - ssh(ji,jj,Kmm)
      END_2D

      DO_3D( 1, 1, 1, 1, 2, jpk )
         zdept(ji,jj,jk) = zdept(ji,jj,jk-1) + e3w(ji,jj,jk,Kmm)
      END_3D

      fsp(:,:,:) = zrhh (:,:,:)
      xsp(:,:,:) = zdept(:,:,:)

      ! Construct the vertical density profile with the
      ! constrained cubic spline interpolation
      ! rho(z) = asp + bsp*z + csp*z^2 + dsp*z^3
      CALL cspline( fsp, xsp, asp, bsp, csp, dsp, polynomial_type )

      ! Integrate the hydrostatic pressure "zhpi(:,:,:)" at "T(ji,jj,1)"
      DO_2D( 0, 1, 0, 1 )
         zrhdt1 = zrhh(ji,jj,1) - interp3( zdept(ji,jj,1), asp(ji,jj,1), bsp(ji,jj,1),  &
            &                                              csp(ji,jj,1), dsp(ji,jj,1) ) * 0.25_wp * e3w(ji,jj,1,Kmm)

         ! assuming linear profile across the top half surface layer
         zhpi(ji,jj,1) =  0.5_wp * e3w(ji,jj,1,Kmm) * zrhdt1
      END_2D

      ! Calculate the pressure "zhpi(:,:,:)" at "T(ji,jj,2:jpkm1)"
      DO_3D( 0, 1, 0, 1, 2, jpkm1 )
         zhpi(ji,jj,jk) = zhpi(ji,jj,jk-1) +                                  &
            &             integ_spline( zdept(ji,jj,jk-1), zdept(ji,jj,jk),   &
            &                           asp  (ji,jj,jk-1), bsp  (ji,jj,jk-1), &
            &                           csp  (ji,jj,jk-1), dsp  (ji,jj,jk-1)  )
      END_3D

      ! Z coordinate of U(ji,jj,1:jpkm1) and V(ji,jj,1:jpkm1)

      ! Prepare zsshu_n and zsshv_n
      DO_2D( 0, 0, 0, 0 )
!!gm BUG ?    if it is ssh at u- & v-point then it should be:
!          zsshu_n(ji,jj) = (e1e2t(ji,jj) * ssh(ji,jj,Kmm) + e1e2t(ji+1,jj) * ssh(ji+1,jj,Kmm)) * &
!                         & r1_e1e2u(ji,jj) * umask(ji,jj,1) * 0.5_wp 
!          zsshv_n(ji,jj) = (e1e2t(ji,jj) * ssh(ji,jj,Kmm) + e1e2t(ji,jj+1) * ssh(ji,jj+1,Kmm)) * &
!                         & r1_e1e2v(ji,jj) * vmask(ji,jj,1) * 0.5_wp 
!!gm not this:
         zsshu_n(ji,jj) = (e1e2u(ji,jj) * ssh(ji,jj,Kmm) + e1e2u(ji+1, jj) * ssh(ji+1,jj,Kmm)) * &
                        & r1_e1e2u(ji,jj) * umask(ji,jj,1) * 0.5_wp
         zsshv_n(ji,jj) = (e1e2v(ji,jj) * ssh(ji,jj,Kmm) + e1e2v(ji+1, jj) * ssh(ji,jj+1,Kmm)) * &
                        & r1_e1e2v(ji,jj) * vmask(ji,jj,1) * 0.5_wp
      END_2D

      DO_2D( 0, 0, 0, 0 )
         zu(ji,jj,1) = - ( e3u(ji,jj,1,Kmm) - zsshu_n(ji,jj) )
         zv(ji,jj,1) = - ( e3v(ji,jj,1,Kmm) - zsshv_n(ji,jj) )
      END_2D

      DO_3D( 0, 0, 0, 0, 2, jpkm1 )
         zu(ji,jj,jk) = zu(ji,jj,jk-1) - e3u(ji,jj,jk,Kmm)
         zv(ji,jj,jk) = zv(ji,jj,jk-1) - e3v(ji,jj,jk,Kmm)
      END_3D

      DO_3D( 0, 0, 0, 0, 1, jpkm1 )
         zu(ji,jj,jk) = zu(ji,jj,jk) + 0.5_wp * e3u(ji,jj,jk,Kmm)
         zv(ji,jj,jk) = zv(ji,jj,jk) + 0.5_wp * e3v(ji,jj,jk,Kmm)
      END_3D

      DO_3D( 0, 0, 0, 0, 1, jpkm1 )
         zu(ji,jj,jk) = MIN(  zu(ji,jj,jk) , MAX( -zdept(ji,jj,jk) , -zdept(ji+1,jj,jk) )  )
         zu(ji,jj,jk) = MAX(  zu(ji,jj,jk) , MIN( -zdept(ji,jj,jk) , -zdept(ji+1,jj,jk) )  )
         zv(ji,jj,jk) = MIN(  zv(ji,jj,jk) , MAX( -zdept(ji,jj,jk) , -zdept(ji,jj+1,jk) )  )
         zv(ji,jj,jk) = MAX(  zv(ji,jj,jk) , MIN( -zdept(ji,jj,jk) , -zdept(ji,jj+1,jk) )  )
      END_3D


      DO_3D( 0, 0, 0, 0, 1, jpkm1 )
         zpwes = 0._wp; zpwed = 0._wp
         zpnss = 0._wp; zpnsd = 0._wp
         zuijk = zu(ji,jj,jk)
         zvijk = zv(ji,jj,jk)

         !!!!!     for u equation
         IF( jk <= mbku(ji,jj) ) THEN
            IF( -zdept(ji+1,jj,jk) >= -zdept(ji,jj,jk) ) THEN
              jis = ji + 1; jid = ji
            ELSE
              jis = ji;     jid = ji +1
            ENDIF

            ! integrate the pressure on the shallow side
            jk1 = jk
            DO WHILE ( -zdept(jis,jj,jk1) > zuijk )
               IF( jk1 == mbku(ji,jj) ) THEN
                  zuijk = -zdept(jis,jj,jk1)
                  EXIT
               ENDIF
               zdeps = MIN(zdept(jis,jj,jk1+1), -zuijk)
               zpwes = zpwes +                                      &
                  integ_spline(zdept(jis,jj,jk1), zdeps,            &
                                 asp(jis,jj,jk1), bsp(jis,jj,jk1),  &
                                 csp(jis,jj,jk1), dsp(jis,jj,jk1))
               jk1 = jk1 + 1
            END DO

            ! integrate the pressure on the deep side
            jk1 = jk
            DO WHILE ( -zdept(jid,jj,jk1) < zuijk )
               IF( jk1 == 1 ) THEN
                  zdeps = zdept(jid,jj,1) + MIN(zuijk, ssh(jid,jj,Kmm)*znad)
                  zrhdt1 = zrhh(jid,jj,1) - interp3(zdept(jid,jj,1), asp(jid,jj,1), &
                                                    bsp(jid,jj,1)  , csp(jid,jj,1), &
                                                    dsp(jid,jj,1)) * zdeps
                  zpwed  = zpwed + 0.5_wp * (zrhh(jid,jj,1) + zrhdt1) * zdeps
                  EXIT
               ENDIF
               zdeps = MAX(zdept(jid,jj,jk1-1), -zuijk)
               zpwed = zpwed +                                        &
                  integ_spline(zdeps,             zdept(jid,jj,jk1),  &
                               asp(jid,jj,jk1-1), bsp(jid,jj,jk1-1),  &
                               csp(jid,jj,jk1-1), dsp(jid,jj,jk1-1) )
               jk1 = jk1 - 1
            END DO

            ! update the momentum trends in u direction
            zdpdx1 = zcoef0 * r1_e1u(ji,jj) * ( zhpi(ji+1,jj,jk) - zhpi(ji,jj,jk) )
            IF( .NOT.ln_linssh ) THEN
               zdpdx2 = zcoef0 * r1_e1u(ji,jj) * &
                  &    ( REAL(jis-jid, wp) * (zpwes + zpwed) + (ssh(ji+1,jj,Kmm)-ssh(ji,jj,Kmm)) )
            ELSE
               zdpdx2 = zcoef0 * r1_e1u(ji,jj) * REAL(jis-jid, wp) * (zpwes + zpwed)
            ENDIF
            IF( ln_wd_il ) THEN
               zdpdx1 = zdpdx1 * zcpx(ji,jj) * wdrampu(ji,jj)
               zdpdx2 = zdpdx2 * zcpx(ji,jj) * wdrampu(ji,jj)
            ENDIF
            puu(ji,jj,jk,Krhs) = puu(ji,jj,jk,Krhs) + (zdpdx1 + zdpdx2 - zpgu(ji,jj)) * umask(ji,jj,jk)
         ENDIF

         !!!!!     for v equation
         IF( jk <= mbkv(ji,jj) ) THEN
            IF( -zdept(ji,jj+1,jk) >= -zdept(ji,jj,jk) ) THEN
               jjs = jj + 1; jjd = jj
            ELSE
               jjs = jj    ; jjd = jj + 1
            ENDIF

            ! integrate the pressure on the shallow side
            jk1 = jk
            DO WHILE ( -zdept(ji,jjs,jk1) > zvijk )
               IF( jk1 == mbkv(ji,jj) ) THEN
                  zvijk = -zdept(ji,jjs,jk1)
                  EXIT
               ENDIF
               zdeps = MIN(zdept(ji,jjs,jk1+1), -zvijk)
               zpnss = zpnss +                                       &
                  integ_spline(zdept(ji,jjs,jk1), zdeps,             &
                               asp(ji,jjs,jk1),   bsp(ji,jjs,jk1),   &
                               csp(ji,jjs,jk1),   dsp(ji,jjs,jk1) )
              jk1 = jk1 + 1
            END DO

            ! integrate the pressure on the deep side
            jk1 = jk
            DO WHILE ( -zdept(ji,jjd,jk1) < zvijk )
               IF( jk1 == 1 ) THEN
                  zdeps = zdept(ji,jjd,1) + MIN(zvijk, ssh(ji,jjd,Kmm)*znad)
                  zrhdt1 = zrhh(ji,jjd,1) - interp3(zdept(ji,jjd,1), asp(ji,jjd,1), &
                                                    bsp(ji,jjd,1)  , csp(ji,jjd,1), &
                                                    dsp(ji,jjd,1) ) * zdeps
                  zpnsd  = zpnsd + 0.5_wp * (zrhh(ji,jjd,1) + zrhdt1) * zdeps
                  EXIT
               ENDIF
               zdeps = MAX(zdept(ji,jjd,jk1-1), -zvijk)
               zpnsd = zpnsd +                                        &
                  integ_spline(zdeps,             zdept(ji,jjd,jk1),  &
                               asp(ji,jjd,jk1-1), bsp(ji,jjd,jk1-1),  &
                               csp(ji,jjd,jk1-1), dsp(ji,jjd,jk1-1) )
               jk1 = jk1 - 1
            END DO

            ! update the momentum trends in v direction
            zdpdy1 = zcoef0 * r1_e2v(ji,jj) * ( zhpi(ji,jj+1,jk) - zhpi(ji,jj,jk) )
            IF( .NOT.ln_linssh ) THEN
               zdpdy2 = zcoef0 * r1_e2v(ji,jj) * &
                       ( REAL(jjs-jjd, wp) * (zpnss + zpnsd) + (ssh(ji,jj+1,Kmm)-ssh(ji,jj,Kmm)) )
            ELSE
               zdpdy2 = zcoef0 * r1_e2v(ji,jj) * REAL(jjs-jjd, wp) * (zpnss + zpnsd )
            ENDIF
            IF( ln_wd_il ) THEN
               zdpdy1 = zdpdy1 * zcpy(ji,jj) * wdrampv(ji,jj)
               zdpdy2 = zdpdy2 * zcpy(ji,jj) * wdrampv(ji,jj)
            ENDIF

            pvv(ji,jj,jk,Krhs) = pvv(ji,jj,jk,Krhs) + (zdpdy1 + zdpdy2 - zpgv(ji,jj)) * vmask(ji,jj,jk)
         ENDIF
         !
      END_3D
      !
      IF( ln_wd_il )   DEALLOCATE( zcpx, zcpy )
      !
   END SUBROUTINE hpg_prj


   SUBROUTINE cspline( fsp, xsp, asp, bsp, csp, dsp, polynomial_type )
      !!----------------------------------------------------------------------
      !!                 ***  ROUTINE cspline  ***
      !!
      !! ** Purpose :   constrained cubic spline interpolation
      !!
      !! ** Method  :   f(x) = asp + bsp*x + csp*x^2 + dsp*x^3
      !!
      !! Reference: CJC Kruger, Constrained Cubic Spline Interpoltation
      !!----------------------------------------------------------------------
      REAL(wp), DIMENSION(A2D(nn_hls),jpk), INTENT(in   ) ::   fsp, xsp           ! value and coordinate
      REAL(wp), DIMENSION(A2D(nn_hls),jpk), INTENT(  out) ::   asp, bsp, csp, dsp ! coefficients of the interpoated function
      INTEGER                             , INTENT(in   ) ::   polynomial_type    ! 1: cubic spline   ;   2: Linear
      !
      INTEGER  ::   ji, jj, jk                 ! dummy loop indices
      REAL(wp) ::   zdf1, zdf2, zddf1, zddf2, ztmp1, ztmp2, zdxtmp
      REAL(wp) ::   zdxtmp1, zdxtmp2, zalpha
      REAL(wp) ::   zdf(jpk)
      !!----------------------------------------------------------------------
      !
      IF (polynomial_type == 1) THEN     ! Constrained Cubic Spline
         DO_2D( 1, 1, 1, 1 )
            !!Fritsch&Butland's method, 1984 (preferred, but more computation)
            !    DO jk = 2, jpkm1-1
            !       zdxtmp1 = xsp(ji,jj,jk)   - xsp(ji,jj,jk-1)
            !       zdxtmp2 = xsp(ji,jj,jk+1) - xsp(ji,jj,jk)
            !       zdf1    = ( fsp(ji,jj,jk)   - fsp(ji,jj,jk-1) ) / zdxtmp1
            !       zdf2    = ( fsp(ji,jj,jk+1) - fsp(ji,jj,jk)   ) / zdxtmp2
            !
            !       zalpha = ( zdxtmp1 + 2._wp * zdxtmp2 ) / ( zdxtmp1 + zdxtmp2 ) / 3._wp
            !
            !       IF(zdf1 * zdf2 <= 0._wp) THEN
            !           zdf(jk) = 0._wp
            !       ELSE
            !         zdf(jk) = zdf1 * zdf2 / ( ( 1._wp - zalpha ) * zdf1 + zalpha * zdf2 )
            !       ENDIF
            !    END DO

            !!Simply geometric average
            DO jk = 2, jpk-2
               zdf1 = (fsp(ji,jj,jk  ) - fsp(ji,jj,jk-1)) / (xsp(ji,jj,jk  ) - xsp(ji,jj,jk-1))
               zdf2 = (fsp(ji,jj,jk+1) - fsp(ji,jj,jk  )) / (xsp(ji,jj,jk+1) - xsp(ji,jj,jk  ))

               IF(zdf1 * zdf2 <= 0._wp) THEN
                  zdf(jk) = 0._wp
               ELSE
                  zdf(jk) = 2._wp * zdf1 * zdf2 / (zdf1 + zdf2)
               ENDIF
            END DO

            zdf(1)     = 1.5_wp * ( fsp(ji,jj,2) - fsp(ji,jj,1) ) / &
                       &          ( xsp(ji,jj,2) - xsp(ji,jj,1) )           -  0.5_wp * zdf(2)
            zdf(jpkm1) = 1.5_wp * ( fsp(ji,jj,jpkm1) - fsp(ji,jj,jpkm1-1) ) / &
                       &          ( xsp(ji,jj,jpkm1) - xsp(ji,jj,jpkm1-1) ) - 0.5_wp * zdf(jpk - 2)

            DO jk = 1, jpk-2
               zdxtmp = xsp(ji,jj,jk+1) - xsp(ji,jj,jk)
               ztmp1  = (zdf(jk+1) + 2._wp * zdf(jk)) / zdxtmp
               ztmp2  =  6._wp * (fsp(ji,jj,jk+1) - fsp(ji,jj,jk)) / zdxtmp / zdxtmp
               zddf1  = -2._wp * ztmp1 + ztmp2
               ztmp1  = (2._wp * zdf(jk+1) + zdf(jk)) / zdxtmp
               zddf2  =  2._wp * ztmp1 - ztmp2

               dsp(ji,jj,jk) = (zddf2 - zddf1) / 6._wp / zdxtmp
               csp(ji,jj,jk) = ( xsp(ji,jj,jk+1) * zddf1 - xsp(ji,jj,jk)*zddf2 ) / 2._wp / zdxtmp
               bsp(ji,jj,jk) = ( fsp(ji,jj,jk+1) - fsp(ji,jj,jk) ) / zdxtmp - &
                             & csp(ji,jj,jk) * ( xsp(ji,jj,jk+1) + xsp(ji,jj,jk) ) - &
                             & dsp(ji,jj,jk) * ((xsp(ji,jj,jk+1) + xsp(ji,jj,jk))**2 - &
                             &                   xsp(ji,jj,jk+1) * xsp(ji,jj,jk))
               asp(ji,jj,jk) = fsp(ji,jj,jk) - xsp(ji,jj,jk) * (bsp(ji,jj,jk) + &
                             &                (xsp(ji,jj,jk) * (csp(ji,jj,jk) + &
                             &                 dsp(ji,jj,jk) * xsp(ji,jj,jk))))
            END DO
         END_2D

      ELSEIF ( polynomial_type == 2 ) THEN     ! Linear
         DO_3D( 1, 1, 1, 1, 1, jpk-2 )
            zdxtmp =xsp(ji,jj,jk+1) - xsp(ji,jj,jk)
            ztmp1 = fsp(ji,jj,jk+1) - fsp(ji,jj,jk)

            dsp(ji,jj,jk) = 0._wp
            csp(ji,jj,jk) = 0._wp
            bsp(ji,jj,jk) = ztmp1 / zdxtmp
            asp(ji,jj,jk) = fsp(ji,jj,jk) - bsp(ji,jj,jk) * xsp(ji,jj,jk)
         END_3D
         !
      ELSE
         CALL ctl_stop( 'invalid polynomial type in cspline' )
      ENDIF
      !
   END SUBROUTINE cspline


   FUNCTION interp1(x, xl, xr, fl, fr)  RESULT(f)
      !!----------------------------------------------------------------------
      !!                 ***  ROUTINE interp1  ***
      !!
      !! ** Purpose :   1-d linear interpolation
      !!
      !! ** Method  :   interpolation is straight forward
      !!                extrapolation is also permitted (no value limit)
      !!----------------------------------------------------------------------
      REAL(wp), INTENT(in) ::  x, xl, xr, fl, fr
      REAL(wp)             ::  f ! result of the interpolation (extrapolation)
      REAL(wp)             ::  zdeltx
      !!----------------------------------------------------------------------
      !
      zdeltx = xr - xl
      IF( abs(zdeltx) <= 10._wp * EPSILON(x) ) THEN
         f = 0.5_wp * (fl + fr)
      ELSE
         f = ( (x - xl ) * fr - ( x - xr ) * fl ) / zdeltx
      ENDIF
      !
   END FUNCTION interp1


   FUNCTION interp2( x, a, b, c, d )  RESULT(f)
      !!----------------------------------------------------------------------
      !!                 ***  ROUTINE interp1  ***
      !!
      !! ** Purpose :   1-d constrained cubic spline interpolation
      !!
      !! ** Method  :  cubic spline interpolation
      !!
      !!----------------------------------------------------------------------
      REAL(wp), INTENT(in) ::  x, a, b, c, d
      REAL(wp)             ::  f ! value from the interpolation
      !!----------------------------------------------------------------------
      !
      f = a + x* ( b + x * ( c + d * x ) )
      !
   END FUNCTION interp2


   FUNCTION interp3( x, a, b, c, d )  RESULT(f)
      !!----------------------------------------------------------------------
      !!                 ***  ROUTINE interp1  ***
      !!
      !! ** Purpose :   Calculate the first order of derivative of
      !!                a cubic spline function y=a+b*x+c*x^2+d*x^3
      !!
      !! ** Method  :   f=dy/dx=b+2*c*x+3*d*x^2
      !!
      !!----------------------------------------------------------------------
      REAL(wp), INTENT(in) ::  x, a, b, c, d
      REAL(wp)             ::  f ! value from the interpolation
      !!----------------------------------------------------------------------
      !
      f = b + x * ( 2._wp * c + 3._wp * d * x)
      !
   END FUNCTION interp3


   FUNCTION integ_spline( xl, xr, a, b, c, d )  RESULT(f)
      !!----------------------------------------------------------------------
      !!                 ***  ROUTINE interp1  ***
      !!
      !! ** Purpose :   1-d constrained cubic spline integration
      !!
      !! ** Method  :  integrate polynomial a+bx+cx^2+dx^3 from xl to xr
      !!
      !!----------------------------------------------------------------------
      REAL(wp), INTENT(in) ::  xl, xr, a, b, c, d
      REAL(wp)             ::  za1, za2, za3
      REAL(wp)             ::  f                   ! integration result
      !!----------------------------------------------------------------------
      !
      za1 = 0.5_wp * b
      za2 = c / 3.0_wp
      za3 = 0.25_wp * d
      !
      f  = xr * ( a + xr * ( za1 + xr * ( za2 + za3 * xr ) ) ) - &
         & xl * ( a + xl * ( za1 + xl * ( za2 + za3 * xl ) ) )
      !
   END FUNCTION integ_spline

   !!======================================================================
END MODULE dynhpg