#include "dims.h"
      SUBROUTINE ADVEC(NX,S,idebug)
      use cons_module,only: long,dlamda_2div3,dlamda_1div12,
     |  dphi_1div12,re_inv
      implicit none
#include "params.h"
#include "fcom.h"
#include "cadvec.h"
#include "buff.h"
#include "index.h"
#include "phys.h"
!
! Args:
      integer,intent(in) :: nx,idebug
      real,intent(out) :: S(1)
!
! Local:
      integer :: nuk,i,nxk,nvjpk,nvjmk,nxjpk,nxjmk

!     if (idebug > 0) then
!       write(6,"('advec: lat=',i2,' save F_IN.')") j
!       call addfsech('F_IN',' ',' ',f(1,nj+nx),zimxp,zkmxp,zkmx,j)
!     endif
C
C     ****                   COMPUTE  X = RACS*DL(X)
C
C     ****                   UBARL = (U(I+1)+U(I-1))/2
      NUK   = NJ+NU
      do i=1,long
        ubarl(i) = (f(i+3,nuk)+f(i+1,nuk))*0.5
      enddo

!     if (idebug > 0)
!    |  call addfsech('UBARL',' ',' ',ubarl,zimxp,zkmxp,zkmx,j)

C                            D2X = dlamda_2div3*(X(I+1)-X(I-1))
      NXK    = NJ+NX
      do i=1,long
        d2x(i) = (f(i+3,nxk)-f(i+1,nxk))*dlamda_2div3
      enddo

!     if (idebug > 0)
!    |  call addfsech('D2X',' ',' ',d2x,zimxp,zkmxp,zkmx,j)

C     ****                   D2X = D2X*UBARL
      do i=1,long
        d2x(i) = d2x(i)*ubarl(i)
      enddo
C     ****                   UBARL = (U(I+2)+U(I-2))/2
      do i=1,long
        ubarl(i) = (f(i+4,nuk)+f(i,nuk))*0.5
      enddo
C     ****                   D4X = dlamda_1div12*(X(I+2)-X(I-2))
      do i=1,long
        d4x(i) = (f(i+4,nxk)-f(i,nxk))*dlamda_1div12
      enddo

!     if (idebug > 0)
!    |  call addfsech('D4X',' ',' ',d4x,zimxp,zkmxp,zkmx,j)

C     ****                   D4X = D4X*UBAR2L
      do i=1,long
        d4x(i) = d4x(i)*ubarl(i)
      enddo

!     if (idebug > 0)
!    |  call addfsech('D4X',' ',' ',d4x,zimxp,zkmxp,zkmx,j)

C     ****                   X = (D2X-D4X)*RACS
      do i=1,long
        x(i) = (d2x(i)-d4x(i))*racs
      enddo

!     if (idebug > 0)
!    |  call addfsech('WK',' ',' ',x,zimxp,zkmxp,zkmx,j)
C
C     ****                   COMPUTE  re_inv*DP(X)
C
C                            VBARP = (V(J+1)+V(J-1))/2
      NVJPK = NJP2+NV
      NVJMK = NJM2+NV
      do i=1,long
        vbarp(i) = (f(i+2,nvjpk)+f(i+2,nvjmk))*0.5
      enddo

!     if (idebug > 0)
!    |  call addfsech('VBARP',' ',' ',vbarp,zimxp,zkmxp,zkmx,j)

C     ****                   D4X = dphi_1div12*(X(J+2)-X(J-2))
      NXJPK = NJP2+NX
      NXJMK = NJM2+NX
      do i=1,long
        d4x(i) = (f(i+2,nxjpk)-f(i+2,nxjmk))*dphi_1div12
      enddo

!     if (idebug > 0)
!    |  call addfsech('D4XJ',' ',' ',d4x,zimxp,zkmxp,zkmx,j)

C     ****                   D4X = D4X*VBARP
      do i=1,long
        d4x(i) = d4x(i)*vbarp(i)
      enddo

!     if (idebug > 0)
!    |  call addfsech('D4XJ',' ',' ',d4x,zimxp,zkmxp,zkmx,j)

C     ****                   D2X = (D2X-D4X)*re_inv
      do i=1,long
        d2x(i) = (d2x(i)-d4x(i))*re_inv
      enddo

!     if (idebug > 0)
!    |  call addfsech('D2XJ',' ',' ',d2x,zimxp,zkmxp,zkmx,j)

C     ****                   S = X+D2X = ADVEC(X)
      do i=1,long
        s(i+2) = x(i)+d2x(i)
      enddo

!     if (idebug > 0)
!    |  call addfsech('HADVEC',' ',' ',s,zimxp,zkmxp,zkmx,j)

      RETURN
      END
C