OPTION ANGLE DEGREES
PRINT
PRINT "＜ アインシュタインの楕円球空間 ＞"
PRINT "        光の６割の速さで移動している観察者が見た"
PRINT "        球の中心で一瞬放たれた光が"
PRINT "        球の内面で反射して中心に帰ってくるまでの光景"
PRINT "        （ 球は相対的な移動方向につぶれている ）"
PRINT

LET X1=3
LET Y1=0
LET X3=-3
LET Y3=0

LET X2=5
LET Y2=0
LET W1=ATN((Y2-Y1)/(X2-X1))
LET W2=ATN((Y3-Y2)/(X3-X2))
DEF zx1=h*COS(W1)+X1
DEF zy2=h*SIN(W1)+Y1
DEF zx3=-1*(h-2)*COS(W2)+X2
DEF zy4=-1*(h-2)*SIN(W2)+Y2

LET X12=0
LET Y12=4
LET W11=ATN((Y12-Y1)/(X12-X1))
LET W12=ATN((Y3-Y12)/(X3-X12))
DEF zx11=-1*h*COS(W11)+X1
DEF zy12=-1*h*SIN(W11)+Y1
DEF zx13=-1*(h-5)*COS(W12)+X12
DEF zy14=-1*(h-5)*SIN(W12)+Y12

LET t=30
LET X22=5*COS(t)
LET Y22=4*SIN(t)
LET h20=SQR ((5*COS(t)-3)^2+(4*SIN(t))^2)
LET W21=ATN((Y22-Y1)/(X22-X1))
LET W22=ATN((Y3-Y22)/(X3-X22))
DEF zx21=h*COS(W21)+X1
DEF zy22=h*SIN(W21)+Y1
DEF zx23=-1*(h-h20)*COS(W22)+X22
DEF zy24=-1*(h-h20)*SIN(W22)+Y22

LET t=60
LET X32=5*COS(t)
LET Y32=4*SIN(t)
LET h30=SQR ((5*COS(t)-3)^2+(4*SIN(t))^2)
LET W31=ATN((Y32-Y1)/(X32-X1))
LET W32=ATN((Y3-Y32)/(X3-X32))
DEF zx31=-1*h*COS(W31)+X1
DEF zy32=-1*h*SIN(W31)+Y1
DEF zx33=-1*(h-h30)*COS(W32)+X32
DEF zy34=-1*(h-h30)*SIN(W32)+Y32

LET t=120
LET X42=5*COS(t)
LET Y42=4*SIN(t)
LET h40=SQR ((5*COS(t)-3)^2+(4*SIN(t))^2)
LET W41=ATN((Y42-Y1)/(X42-X1))
LET W42=ATN((Y3-Y42)/(X3-X42))
DEF zx41=-1*h*COS(W41)+X1
DEF zy42=-1*h*SIN(W41)+Y1
DEF zx43=-1*(h-h40)*COS(W42)+X42
DEF zy44=-1*(h-h40)*SIN(W42)+Y42

LET t=150
LET X52=5*COS(t)
LET Y52=4*SIN(t)
LET h50=SQR ((5*COS(t)-3)^2+(4*SIN(t))^2)
LET W51=ATN((Y52-Y1)/(X52-X1))
LET W52=ATN((Y3-Y52)/(X3-X52))
DEF zx51=-1*h*COS(W51)+X1
DEF zy52=-1*h*SIN(W51)+Y1
DEF zx53=(h-h50)*COS(W52)+X52
DEF zy54=(h-h50)*SIN(W52)+Y52

LET X62=-5
LET Y62=0
LET W61=ATN((Y62-Y1)/(X62-X1))
LET W62=ATN((Y3-Y62)/(X3-X62))
DEF zx61=-1*h*COS(W61)+X1
DEF zy62=-1*h*SIN(W61)+Y1
DEF zx63=(h-8)*COS(W62)+X62
DEF zy64=(h-8)*SIN(W62)+Y62

SET WINDOW -7,7,-7,7
DRAW GRID
DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(3,0)
DRAW CIRCLE WITH  SCALE(3.2,4)*SHIFT(3,0)
WAIT DELAY 1
FOR h=0 TO 10 STEP 0.1
   SET DRAW mode hidden       ! ちらつき防止
   CLEAR
   DRAW GRID
   DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(3,0)
   DRAW CIRCLE WITH SCALE(3.2,4)*SHIFT(3-0.6*h,0)
    
   IF h=<2 THEN 
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx1,zy2)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(5,0)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx3,zy4)
   END IF
   WAIT DELAY 0.1
    
   IF h=<5 THEN
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx11,zy12)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(0,4)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx13,zy14)
   END IF
   WAIT DELAY 0.1
    
   IF h=<h20 THEN
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx21,zy22)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(X22,Y22)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx23,zy24)
   END IF
   WAIT DELAY 0.1
    
   IF h=<h30 THEN
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx31,zy32)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(X32,Y32)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx33,zy34)
   END IF
    
   IF h=<h40 THEN
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx41,zy42)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(X42,Y42)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx43,zy44)
   END IF
   WAIT DELAY 0.1
    
   IF h=<h50 THEN
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx51,zy52)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(X52,Y52)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx53,zy54)
   END IF    
   WAIT DELAY 0.1
    
   IF h=<8 THEN
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx61,zy62)
   ELSE
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(X62,Y62)
      DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(zx63,zy64)
   END IF    
   WAIT DELAY 0.1
    
   SET DRAW mode explicit   ! ちらつき防止 
NEXT h

DRAW DISK WITH SCALE(0.1,0.1)*SHIFT(-3,0)
DRAW CIRCLE WITH  SCALE(3.2,4)*SHIFT(3,0)
DEF XX(t)=5*COS(t)
DEF YY(t)=4*SIN(t)
SET LINE WIDTH 3
FOR t=0 TO 360
   PLOT LINES: XX(t),YY(t);   ! 媒介変数
NEXT t
PLOT LINES
PRINT
END