SUBROUTINE  VISDS (Z1,ZE,Z2,J1,J2,MX,I1,I2,MY,US,VS,L,M,PL)

C     [DIAGONAL 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   MAXNMA 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     [06-OCT-74]

      EXTERNAL    PL
      DIMENSION   ZE(1),U(501),V(501)
      DATA        MK/501/

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

      NL=ISIGN(1,L)
      NM=ISIGN(1,M)
      N=NL*NM
      IL=I1-IABS(M)
      IU=I2+IABS(M)
      MM=1
      TE=0.5*FLOAT(NL+1)
      ZS=(1.0-VS)/(Z2-Z1)
      DUI=-(FLOAT(NL)*US)/FLOAT(MY-1)
      EUI=DUI*FLOAT(M)
      DUJ=(1.0-US)/FLOAT(MX-1)
      EUJ=DUJ*FLOAT(L)
      DVI=VS/FLOAT(MY-1)
      EVI=DVI*FLOAT(M)
      I0=(I2+I1-NM*(I2-I1))/2+M
      J0=(J2+J1-NL*(J2-J1))/2
      K0=((MK+1)*(1-N))/2
   10 K=K0
      I=MAX0(MIN0(I0,IU),IL)
      J=J0
      EU=TE*US+DUI*FLOAT(I-1)+DUJ*FLOAT(J-1)
      VE=      DVI*FLOAT(I-1)
   20 IF ((I.LT.I1).OR.(I.GT.I2)) 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-EUI
      VE=VE-EVI
      IF ((I.LT.I1).OR.(I.GT.I2)) 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+EUJ
      IF ((J.GE.J1).AND.(J.LE.J2)) GO TO 20
   30 KK=(K+1-N*(K-1))/2
      CALL VISHO (U(KK),V(KK),(MK+1-N*(MK-2*K+1))/2,MM,PL)
      MM=-MM
      I0=I0+M
      IF ((I0.GE.IL).AND.(I0.LE.IU)) GO TO 10
      J0=J0+L
      IF ((J0.GE.J1).AND.(J0.LE.J2)) GO TO 10
      RETURN

      END