SET WINDOW -1.1,1.1,-1.1,1.1
LET a=2
LET b=1
LET Q1=a/(a+b)
LET Q2=b/(a+b)
FOR x=1 TO -1 STEP -0.01
   SET DRAW mode hidden ! ちらつき防止の特殊処理(1)
   CLEAR
   IF x > 0.7 THEN
      FOR i=1 TO x STEP -0.001
         DRAW disk WITH SCALE(0.005)*SHIFT(i*Q1,SQR(1-i^2)*Q2)
      NEXT i
   ELSE
      FOR i=x+0.3 TO x STEP -0.001
         DRAW disk WITH SCALE(0.005)*SHIFT(i*Q1,SQR(1-i^2)*Q2)
      NEXT i
   END IF
   DRAW AXES
   SET LINE width 2
   SET COLOR 4
   LET y = SQR(1-x^2)
   PLOT LINES: x,0;0,y
   DRAW disk WITH SCALE(0.02)*SHIFT(x*Q1,Y*Q2)
   WAIT DELAY 0.01-0.001*t
   SET DRAW mode explicit ! ちらつき防止の特殊処理(2)
   SET COLOR 1
NEXT x
FOR x=-1 TO 1 STEP 0.01
   SET DRAW mode hidden ! ちらつき防止の特殊処理(1)
   CLEAR
   IF x < -0.7 THEN
      FOR i=-1 TO x STEP 0.001
         DRAW disk WITH SCALE(0.005)*SHIFT(i*Q1,-1*SQR(1-i^2)*Q2)
      NEXT i
   ELSE
      FOR i=x-0.3 TO x STEP 0.001
         DRAW disk WITH SCALE(0.005)*SHIFT(i*Q1,-1*SQR(1-i^2)*Q2)
      NEXT i
   END IF
   DRAW AXES
   SET LINE width 2
   SET COLOR 4
   LET y = SQR(1-x^2)
   PLOT LINES: x,0;0,-1*y
   DRAW disk WITH SCALE(0.02)*SHIFT(x*Q1,-1*Y*Q2)
   WAIT DELAY 0.01
   SET DRAW mode explicit ! ちらつき防止の特殊処理(2)
   SET COLOR 1
NEXT x
FOR i=1 TO -1 STEP -0.001
   DRAW disk WITH SCALE(0.005)*SHIFT(i*Q1,SQR(1-i^2)*Q2)
NEXT i
FOR i=-1 TO 1 STEP 0.001
   DRAW disk WITH SCALE(0.005)*SHIFT(i*Q1,-1*SQR(1-i^2)*Q2)
NEXT i
PLOT TEXT ,AT -0.8,0.8 : "軌跡の楕円"
PLOT TEXT ,AT Q1-0.3,-0.1 : STR$(Q1)
PLOT TEXT ,AT -0.3,Q2+0.05 : STR$(Q2)
END