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!Environment Canada - Atmospheric Science and Technology License/Disclaimer,
!                     version 3; Last Modified: May 7, 2008.
!This is free but copyrighted software; you can use/redistribute/modify it under the terms
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!

      SUBROUTINE VTAPST2(PY,PR,PCON,KLEV,KILG,VMA,VMB,VMC) 1
C
*S/P VTAP:
C         CALCULE Y A PARTIR DE R PAR SOLUTION DE L'EQUATION R*CON=S**E*D(Y)
C         AVEC UN SCHEME DU 4EME ORDRE DU A J. COTE. ON DOIT FOURNIR LA COND
C         A LA LIMITE INF. Y(N). LA MATRICE MATAP A ETE CALCULEE DANS LA
C         SUBR. MATAPAT.
C         NOTE: CET ALGORITHME EST EXACTEMENT REVERSIBLE (VOIR VPAT).
C
C AUTHOR: MICHEL BELAND - AVRIL 1984 - ADAPTE AU MODELE SEF, AVRIL 1984.
C
C REVISION: LUC FILLION - AUG 94 - MODIFIED FOR VARIATIONAL ANALYSIS.
C           Simon Pellerin : Extension to 2D GZ
C ARGUMENTS:
C     PY      : PRIMITIVE
C     PR      : INTEGRAND
C     PCON    : CONSTANTE
C     KLEV    : NOMBRE DE NIVEAUX SIGMA DU MODELE.
C     KILG    : NOMBRE DE LONGITUDES SUR LA GRILLE DE CALCUL.
C
C#endif
      IMPLICIT NONE
      INTEGER  KILG, KLEV
      REAL*8     PY(KILG,KLEV), PR(KILG,KLEV), PCON
      real*8     vma(kilg,klev),vmb(kilg,klev),vmc(kilg,klev)
C
      INTEGER  JLON, IKLEVM2, JK, IK
      REAL*8     ZAK, ZBK, ZCK
*
**
      DO 10 JLON = 1, KILG
        ZAK = -2.0*PCON*VMA(jlon,KLEV)
        ZBK = -2.0*PCON*VMB(jlon,KLEV)
        ZCK = -2.0*PCON*VMC(jlon,KLEV)
        PY(JLON,KLEV-1) = ZAK * PR(JLON,KLEV-1) + ZBK * PR(JLON,KLEV)
     +                    + ZCK * PR(JLON,KLEV-2) + PY(JLON,KLEV)
 10   CONTINUE
      IKLEVM2 = KLEV-2
      DO 30 JK = 1, IKLEVM2
        IK = KLEV-1-JK
        DO 20 JLON = 1, KILG
          ZAK = -2.0*PCON*VMA(jlon,IK+1)
          ZBK = -2.0*PCON*VMB(jlon,IK+1)
          ZCK = -2.0*PCON*VMC(jlon,IK+1)
          PY(JLON,IK) = ZAK * PR(JLON,IK) + ZBK * PR(JLON,IK+1)
     +                  + ZCK * PR(JLON,IK+2) + PY(JLON,IK+2)
 20     CONTINUE
 30   CONTINUE
C
C
      RETURN
      END