蛙跳び

' Leap Frog Method
  dim n as Integer
  dim i as Integer
  dim f(100) as double
  dim fo(100) as double
  dim fn(100) as double
  dim mojiretsu as String

  'Initial Condition
  For i = 1 to ixmx
    if i > 10 And i<20 then
      fo(i) = 1.0
      f(i) = 1.0
      fn(i) = 1.0
    else
      fo(i) = 0.0
      f(i) = 0.0
      fn(i) = 0.0
    end if
  next i
  'Time Marching
  for n =1 to itmx
    'Leap Frog
    for i = 2 to ixmx
      fn(i) = fo(i) - 2*u*dt/dx*(f(i) - f(i-1))
    next i
 
    'Shift Variables
    for i = 2 to ixmx
      f(i) = 0.5*(fn(i)+fo(i))
      fo(i) = fn(i)
    next i
  next n

  'Output
  for i = 1 to ixmx
    mojiretsu = Str(i) +"," + Str(f(i))
    ListBox2.AddRow(mojiretsu)
  next i

4次精度ルンゲクッタと比較すると、2次精度の蛙飛びの方が、鈍りが少ないです。

なぜなんだろう・・・。