C      PROGRAM PTEST(OUTPUT)
C
C         EXAMPLE OF 3D PLOT USAGE
C
      COMMON /CPLT3D/  PHI,YL,XL,ZL,YLINES,BASFLG,ANX(102),
     $ANY(102),SX(25),SY(25),XT(25),XPP(102),YPP(102),FR(512)
C
C         DIMENSION ANX(NY) ANY(NY) XPP(NY) YPP(NY) OR GREATER
C     COMMON /QPEN/ IPEN
      DIMENSION X(50),Y(39),Z(39,50)     !   *** NOTE:  Z(NY,NX) *****
C                                        !        NOT THE REVERSE
C         MAX SQUARE ARRAY FOR PDP/8 IS 44x44
      CALL ALTINT(ALTM)
      ALTM=1.0
      YLINES=1.0
      BASFLG=1.0
      PHI=60.0
      NX=50
      NY=39
C
C
C
      IYES=6HY
      WRITE(4,37)
 37   FORMAT(///,'   TYPE ESC TO CLOSE PLOT FILE ',/)
      WRITE(4,35)
      READ(4,36) IANS
C
 35   FORMAT(//,'  TYPE Y IF CONTINUOUS PLOTTING IS DESIRED ',$)
 36   FORMAT(1A1)
C
C
C         SET UP X-VECTOR
      X(1)=-1.0
      DO 110  I=2,NX
 110  X(I)=X(I-1)+2.0/NX
C
C         SET UP Y-VECTOR
      Y(1)=-1.0+0.25
      DO 120  J=2,NY
 120  Y(J)=Y(J-1)+2.0/NX
C
      WRITE(4,100)
C         COMPUTE Z-MATRIX
      SIGMA=0.3
      S2=-1.0/SIGMA**2
      DO 131  J=1,NY
      DO 130  I=1,NX
      R=X(I)**2+Y(J)**2
      S=SQRT(R)*6.0
      S=0.1*COS(S)
 130  Z(J,I)=EXP(R*S2)+S
 131  CONTINUE
C
 252  FORMAT(4(3X,F12.4))
C
C         CUT A SLICE PARALLEL TO THE Y AXIS
      DO 34  I=24,25     ! Y RUNS FROM Y(24) THRU Y(25)
      DO 34  J=1,NX      ! X RUNS FROM XMIN THRU XMAX
      Z(I,J)=0.0
 34   CONTINUE
C
C         INITIALIZE SYSTEM PLOT ROUTINES
      CALL SPLOT
      CALL FACTOR(.01)
 333  IF(ALTM .EQ. 0.0) STOP
      CALL PLOT(0.0,-30.0,-3)
C
      CALL PLOT3D(X,Y,Z,NX,NY)
      CALL WHERE(XP,YP,FACT)
      CALL SYMBOL(050,YP,14.,9HCUT AT Y=,0.00,9)
      FNP=(Y(24)+Y(25))/2.0
      CALL WHERE(XP,YP,FACT)
      XP=XP+10.
      CALL NUMBER(XP,YP,14.0,FNP,0.00,+2)
C
      IF(IANS .EQ. IYES)  GO TO 29
      CALL PAGE
C
      STOP 24
 29   CALL SPAGE
 100  FORMAT(/////)
      GO TO 333
      STOP 23
      END