SUBROUTINE  VISDC (Z1,ZE,Z2,NZ,NX,MX,NY,MY,US,VS,L,PL)

C     [DIAGONAL CONTOURED SEQUENCE]
C     ZE(J,I) ARRAY OF FUNCTION VALUES
C     (Z1,Z2) SPAN OF Z VALUES
C     NX,NY   RANGES OF J AND I
C     MX,MY   MAXIMA ATTAINABLE BY J AND I
C     US,VS   TOTAL SHEARS IN U AND V DIRECTIONS
C     L       DIRECTION OF VIEW (1=WEST, -1=EAST)
C     PL      PEN MOVEMENT SUBROUTINE
C     [16-MAY-74]

      EXTERNAL    PL
      DIMENSION   ZE(1)
      DIMENSION   A(501),B(501)
      DIMENSION   D(501),E(501),G(501)
      DIMENSION   U(501),V(501),W(501)
      DATA        M,MK/1,501/

      IX(J,I)=(I-1)*MX+J
      SC(Z)=ZS*(Z-Z1)

      NA=0
      ND=0
      N=L*M
      MM=1
      EL=FLOAT(L)
      EM=FLOAT(M)
      TE=0.5*(EL+1.0)
      ZS=(1.0-VS)/(Z2-Z1)
      DZ=(Z2-Z1)/FLOAT(NZ-1)
      DUI=-(EL*US)/FLOAT(MY-1)
      DUJ=(1.0-US)/FLOAT(MX-1)
      DVI=VS/FLOAT(MY-1)

      I0=(NY+1-M*(NY-3))/2
      J0=(NX+1-L*(NX-1))/2
      K0=((MK+1)*(1-N))/2
   10 K=K0
      I=MAX0(MIN0(I0,NY+1),0)
      J=J0
      EU=TE*US+DUI*FLOAT(I-1)+DUJ*FLOAT(J-1)
      VE=      DVI*FLOAT(I-1)
   20 IF ((I.LT.1).OR.(I.GT.NY)) GO TO 22
      K=MAX0(MIN0(K+N,MK),1)
      U(K)=EU
      V(K)=VE+SC(ZE(IX(J,I)))
   22 I=I-M
      EU=EU-DUI
      VE=VE-EM*DVI
      IF ((I.LT.1).OR.(I.GT.NY)) GO TO 30
      K=MAX0(MIN0(K+N,MK),1)
      U(K)=EU
      V(K)=VE+SC(ZE(IX(J,I)))
      J=J+L
      EU=EU+EL*DUJ
      IF ((J.GE.1).AND.(J.LE.NX)) GO TO 20
   30 ZI=Z1
      DO 60 IZ=1,NZ
      K=K0
      I=MAX0(MIN0(I0,NY+1),0)
      J=J0
      EU=TE*US+DUI*FLOAT(I-1)+DUJ*FLOAT(J-1)
      VE=      DVI*FLOAT(I-1)
   40 IF ((I.LT.1).OR.(I.GT.NY)) GO TO 42
      K=MAX0(MIN0(K+N,MK),1)
      W(K)=VE+SC(ZI)
   42 I=I-M
      EU=EU-DUI
      VE=VE-EM*DVI
      IF ((I.LT.1).OR.(I.GT.NY)) GO TO 50
      K=MAX0(MIN0(K+N,MK),1)
      W(K)=VE+SC(ZI)
      J=J+L
      EU=EU+EL*DUJ
      IF ((J.GE.1).AND.(J.LE.NX)) GO TO 40
   50 CALL VISRB (A,B,NA,MK,U,V,K,U,W,K,-1.0)
      CALL VISHH (D,E,G,ND,A,B,NA,MM,PL)
      MM=-MM
   60 ZI=ZI+DZ
      I0=I0+M
      IF ((I0.GE.0).AND.(I0.LE.NY+1)) GO TO 10
      J0=J0+L
      IF ((J0.GE.1).AND.(J0.LE.NX))   GO TO 10
      RETURN

      END