' fsprlib.bas - jackord@kw.igs.net - revised 18 Mar 04 - Liberty Basic v4.00

' Initialize Window
  nomainwin
  WindowWidth=410     ' pixel scale 0-400
  WindowHeight=329    ' pixel scale 0-300
  UpperLeftX=100: UpperLeftY=100
  open "Spring" for graphics_nsb as #1
  #1 "trapclose [quit]"
  #1 "cls ; down ; color blue"
  xsc=400/.83: ysc=300/.23
  m=2: k=200: gr=9.8: dt=.005: ym=0
  t=0: y=0: v=0: a=0-gr-k*y/m                          ' Feynman algorithm
  #1 "place "; int(xsc*(t+.1)); " "; int(ysc*(.02-y))
  v=v+a*dt/2: vo=v
  while vo<0 or v>=0                                   ' test for return
    vo=v: t=t+dt: y=y+v*dt: a=0-gr-k*y/m: v=v+a*dt
    #1 "goto "; int(xsc*(t+.1)); " "; int(ysc*(.02-y))
    if vo<0 and v>=0 then ym=y                         ' test for bottom
  wend
  t=t+dt/2-v/a                                         ' correct time
  #1 "color black ; place 80 15"
  #1 "\Ymin = "; ym; " (expect "; 0-2*m*gr/k; ")"
  #1 "\Yret = "; y; " (expect 0)"
  #1 "\Time = "; t; " (expect "; .8*atn(1); ")"
  wait

[quit]
  close #1
end