interpol_linear.F90

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!SFX_LIC Copyright 1994-2014 CNRS, Meteo-France and Universite Paul Sabatier
!SFX_LIC This is part of the SURFEX software governed by the CeCILL-C licence
!SFX_LIC version 1. See LICENSE, CeCILL-C_V1-en.txt and CeCILL-C_V1-fr.txt  
!SFX_LIC for details. version 1.
!     #########
      SUBROUTINE interpol_linear(PDAT,PNDAT,PVAL0,PVAL1,PVAL2,POUT)
!     #############################################################
!
!!**** *INTERPOL_LINEAR* Linear interpolation between 3 month.
!!                       Current value is reached evry 16 of each month,
!!                       except in February every 15.
!!
!!
!!    PURPOSE
!!    -------
!!
!!    METHOD
!!    ------
!!   
!!    EXTERNAL
!!    --------
!!
!!    IMPLICIT ARGUMENTS
!!    ------------------
!!
!!
!!    REFERENCE
!!    ---------
!!
!!    AUTHOR
!!    ------
!!
!!    B. Decharme         Meteo-France
!!
!!    MODIFICATION
!!    ------------
!!
!!    Original    07/2015
!!
!----------------------------------------------------------------------------
!
!*    0.     DECLARATION
!            -----------
!
USE yomhook   ,ONLY : lhook,   dr_hook
USE parkind1  ,ONLY : jprb
!
IMPLICIT NONE
!
!*    0.1    Declaration of arguments
!            ------------------------
!
REAL,                    INTENT(IN)    :: PDAT    ! Present date in the current month
REAL,                    INTENT(IN)    :: PNDAT   ! Number of date in the current month
REAL, DIMENSION(:),      INTENT(IN)    :: PVAL0   ! Value of the precedent month
REAL, DIMENSION(:),      INTENT(IN)    :: PVAL1   ! Value of the current month
REAL, DIMENSION(:),      INTENT(IN)    :: PVAL2   ! Value of the next month
REAL, DIMENSION(:),      INTENT(OUT)   :: POUT    ! Interpolated value
!
!
!*    0.2    Declaration of other local variables
!            ------------------------------------
!
REAL         :: ZFACT0, ZFACT1, ZFACT2
!
REAL(KIND=JPRB) :: ZHOOK_HANDLE
!
!----------------------------------------------------------------------------
!
!*    0.     Allocation
!            ----------
!
IF (lhook) CALL dr_hook('INTERPOL_LINEAR',0,zhook_handle)
!
!*    1.     Initialization
!            --------------
!
!*    2.     Coef calculation
!            ----------------
!
zfact0=max(1.0-(pdat*2.0+pndat-1.0)/(pndat*2.0),0.0)
zfact1=(2.0*pndat-abs(2.0*pdat-pndat-1.0))/(pndat*2.0)
zfact2=max(1.0-((pndat+1.0-pdat)*2.0+pndat-1.0)/(pndat*2.0),0.0)
!
!*    3.     Final calculation
!            -----------------
!
pout(:) = pval0(:)*zfact0+pval1(:)*zfact1+pval2(:)*zfact2
!
!*    4.     End
!            ---
!
IF (lhook) CALL dr_hook('INTERPOL_LINEAR',1,zhook_handle)
!
!-------------------------------------------------------------------------------
!
END SUBROUTINE interpol_linear