C KAPC21    SOURCE    PV        11/03/07    21:17:10     6885           
      SUBROUTINE  KAPC21(NES,X,A,NR,XR,IFACE,KFACE,KAC)
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8 (A-H,O-Z)                                                 
C
C     CAS DE 2 FACES PARALLELES: DIRECTION KAC                                  
C     ----------------------------------------                                  
C     A   : CENTRE DE L'H.C
C     IFACE : NUMERO DE FACE
C     KFACE : COORDONNEES ENTIERES SUR LA FACE
C
      DIMENSION X(NES),A(NES),XA(2),XR(NES)
C
      NR2 = NR/2
      EPS=1D-5
      XAB = -EPS
      A1 = -1D-10
                                                                                
        DO 1  IES = 1,NES
         XA(IES) = X(IES)-A(IES)
         A2=DABS(XA(IES))
         IF(A2.GT.A1) THEN
           A1 = A2
           I = IES
         ENDIF
 1      CONTINUE
C
      IF (I.EQ.KAC) THEN
        DO 2 IES = 1,NES                                                        
           A2 = DABS(XA(IES))                                                   
           ERR = DABS(1.-A2/A1)                                                 
           IF (IES.EQ.I.AND.ERR.LT.0.01) THEN                                   
           I = IES                                                              
           GOTO 3                                                               
           ENDIF                                                                
 2      CONTINUE                                                                
      ENDIF                                                                     
                                                                                
 3      CONTINUE                                                                
                                                                                
C     WRITE(6,*) 'A1 XA(I) ',A1,XA(I)
      KS = KSIG(XA(I),EPS)
C     WRITE(6,*) ' KS ',KS
C
      IF (I.EQ.1) THEN
           XR(2) = XA(2)/A1
           I1 = 1 + INT(NR2*(1+XR(2)))
           KFACE = MIN0(NR,I1)
           IF(KS.EQ.1) THEN
           IFACE= 1
           XR(1) = 1.
           ELSE
           IFACE = 2
           XR(1) = -1.
           ENDIF
           RETURN
      ENDIF
      IF (I.EQ.2) THEN
           XR(1) = XA(1)/A1
           I1 = 1 + INT(NR2*(1+XR(1)))
           KFACE    = MIN0(NR,I1)
           IF(KS.EQ.1) THEN
           IFACE    = 3
           XR(2) =  1.
           ELSE
           IFACE    = 4
           XR(2) = -1.
           ENDIF
           RETURN
      ENDIF
      END