! spirograph.jnl - cute pictures - *sh* 11/91
! Description: demo of fun line plots

! Clean up from whatever the user has been doing ...
SET GRID abstract
CANCEL VARIABLES/ALL


! Use the straightening of 2D arrays into 1D to quickly create a cute picture.
PLOT/VS/LINE/I=1:50/J=1:50 6*I/J,5*J/I
MESSAGE

! Now define the variable, ODD, to separate odd and even points.
! Then plot alternatine points on the circumference of a circle.
LET ODD = MOD(I,2) EQ 0
LET XPT = IF ODD THEN (-1*SIN(I/100)) ELSE SIN(I/100)
LET YPT = IF ODD THEN COS(I/100) ELSE (-1*COS(I/100))
PLOT/VS/LINE/I=1:314 XPT,YPT
MESSAGE

! Variation on a theme: place the circumference points 10 times
! further apart but go around the circle 10 times.
LET XPT2 = IF ODD THEN (-1*SIN(I/10)) ELSE SIN(I/10)
LET YPT2 = IF ODD THEN COS(I/10) ELSE (-1*COS(I/10))
PLOT/VS/LINE/I=1:314 XPT2,YPT2
MESSAGE

! A bit wilder, still ...
LET XPT3 = IF ODD THEN (-1*SIN(I/10)) ELSE 1/(2+SIN(I/10))
LET YPT3 = IF ODD THEN COS(I/10) ELSE (1/(2+COS(I/10)))
PLOT/VS/LINE/I=1:314 XPT3,YPT3
MESSAGE

! Now for some true art ...
! Move the circle center while drawing circumference points.
LET XCNTR = COS(I/30)
LET YCNTR = SIN(I/30)
LET XPT4 = IF ODD THEN (-1*SIN(I/10)) ELSE SIN(I/10)
LET YPT4 = IF ODD THEN COS(I/10) ELSE (-1*COS(I/10))
LET XPT5 = XPT4 + XCNTR
LET YPT5 = YPT4 + YCNTR
PLOT/VS/LINE/I=1:380 XPT5,YPT5