C $Header: /home/ubuntu/mnt/e9_copy/MITgcm/pkg/shap_filt/shap_filt_u.F,v 1.3 2001/02/04 14:38:50 cnh Exp $
C $Name:  $

#include "SHAP_FILT_OPTIONS.h"

      SUBROUTINE SHAP_FILT_U(uVel,bi,bj,K,myCurrentTime,myThid)
C     /==========================================================\
C     | S/R SHAP_FILT_U                                          |
C     | Applies Shapiro filter to U field over one XY slice      |
C     | of one tile at a time.                                   |
C     \==========================================================/
      IMPLICIT NONE

C     == Global variables ===
#include "SIZE.h"
#include "EEPARAMS.h"
#include "PARAMS.h"
#include "GRID.h"

C     == Routine arguments
      _RL uVel(1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy)
      INTEGER myThid
      _RL     myCurrentTime
      INTEGER bi, bj, K

#ifdef ALLOW_SHAP_FILT

C     == Local variables ==
      _RL tmpFldX(1-OLx:sNx+OLx,1-OLy:sNy+OLy,2)
      _RL tmpFldY(1-OLx:sNx+OLx,1-OLy:sNy+OLy,2)
      _RS maskZ(1-OLx:sNx+OLx,1-OLy:sNy+OLy)
      INTEGER I,J,N,N1,N2

      DO J=1-OLy,sNy+OLy
       DO I=1-OLx,sNx+OLx
        tmpFldX(i,j,1) = uVel(i,j,k,bi,bj)
     &                   *_maskW(i,j,k,bi,bj)
       ENDDO
      ENDDO

C     Extract small-scale noise from tmpFldX (delta_ii^n)
      DO N=1,nShap
       N1=1+mod(N+1,2)
       N2=1+mod( N ,2)
       DO J=1-OLy,sNy+OLy
        DO I=1-OLx+1,sNx+OLx-1
         tmpFldX(i,j,N2) = -0.25*(
     &          tmpFldX(i-1,j,N1) + tmpFldX(i+1,j,N1)
     &             - 2.*tmpFldX(i,j,N1) 
     &            )*_maskW(i,j,k,bi,bj)
        ENDDO
       ENDDO
      ENDDO

C     Create temporary Zeta mask (accounting for thin walls)
      DO J=1-OLy,sNy+OLy
       DO I=1-OLx+1,sNx+OLx
        maskZ(i,j) = _maskS(i-1,j,k,bi,bj)
     &              *_maskS( i ,j,k,bi,bj)
       ENDDO
      ENDDO

#ifdef SEQUENTIAL_2D_SHAP
      DO J=1-OLy,sNy+OLy
       DO I=1-OLx,sNx+OLx
        tmpFldX(i,j,N2) = uVel(i,j,k,bi,bj) - tmpFldX(i,j,N2)
        tmpFldY(i,j,1) = tmpFldX(i,j,N2)
       ENDDO
      ENDDO
#else
      DO J=1-OLy,sNy+OLy
       DO I=1-OLx,sNx+OLx
        tmpFldY(i,j,1) = uVel(i,j,k,bi,bj)
     &                   *_maskW(i,j,k,bi,bj)
       ENDDO
      ENDDO
#endif /* SEQUENTIAL_2D_SHAP */

C     Extract small-scale noise from tmpFldY (delta_jj^n)
      DO N=1,nShap
       N1=1+mod(N+1,2)
       N2=1+mod( N ,2)
       DO J=1-OLy+1,sNy+OLy-1
        DO I=1-OLx+1,sNx+OLx
         tmpFldY(i,j,N2) = -0.25*(
     &    (tmpFldY(i,j+1,N1)-tmpFldY(i, j ,N1))*maskZ(i,j+1)
     &   -(tmpFldY(i, j ,N1)-tmpFldY(i,j-1,N1))*maskZ(i, j )
#ifdef NO_SLIP_SHAP
     &   -2.*(2.-maskZ(i,j)-maskZ(i,j+1))*tmpFldY(i,j,N1)
#endif
     &         )*_maskW(i,j,k,bi,bj)
        ENDDO
       ENDDO
      ENDDO

C     Subtract small-scale noise from field
#ifdef SEQUENTIAL_2D_SHAP
      DO J=1-OLy,sNy+OLy
       DO I=1-OLx,sNx+OLx
        uVel(i,j,k,bi,bj) = tmpFldX(i,j,N2) - tmpFldY(i,j,N2)
       ENDDO
      ENDDO
#else
      DO J=1-OLy,sNy+OLy
       DO I=1-OLx,sNx+OLx
        uVel(i,j,k,bi,bj) = uVel(i,j,k,bi,bj)
     &    -0.5*( tmpFldX(i,j,N2)+tmpFldY(i,j,N2) )
       ENDDO
      ENDDO
#endif /* SEQUENTIAL_2D_SHAP */

#endif /* ALLOW_SHAP_FILT */

      RETURN
      END