' The frames of the animation can be drawn
' by the code below in BASIC. The animation
' is made by collecting the frames in an
' image editor such as GIMP.

REM Constant
pi=4*atn(1)
REM Set up plotting area
screen 12
window (0,-2)-(5*pi,2)

REM Number of terms to use
for nt=1 to 25
 cls
 print "Harmonics:";nt

 REM Plot squarewave
 pset (0,0)
 for w=0 to 5*pi step .01
  line -(w,sgn(sin(w))),4
 next w

 REM Plot sum of terms
 pset (0,0)
 for w=0 to 5*pi step .01
  y=0
  for k=1 to nt
   y=y+sin((2*k-1)*w)/(2*k-1)
  next k
  y=4*y/pi
  line -(w,y)
 next w

 REM Freeze display (create a gif animation frame)
 delay .2
next nt