VERSION 5.00
Begin VB.Form Form18 
   BackColor       =   &H00FFFFFF&
   Caption         =   "歐拉法"
   ClientHeight    =   8700
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   10935
   LinkTopic       =   "Form23"
   ScaleHeight     =   8700
   ScaleWidth      =   10935
   StartUpPosition =   3  '窗口缺省
   Begin VB.CommandButton Command1 
      Caption         =   "歐拉法"
      BeginProperty Font 
         Name            =   "宋體"
         Size            =   10.5
         Charset         =   134
         Weight          =   700
         Underline       =   0   'False
         Italic          =   0   'False
         Strikethrough   =   0   'False
      EndProperty
      Height          =   495
      Left            =   960
      TabIndex        =   0
      Top             =   1080
      Width           =   1215
   End
End
Attribute VB_Name = "Form18"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False

Private Sub Command1_Click()
'衛星的運動方程
' y1'=y3
' y2'=y4
' y3'=y1+2y4-v(y1+u)/r1^3-u(y1-v)/r2^3
' y4'=y2-2y3-vy2/r1^3-vy2/r2^3
'其中v=1-u,r1=[(y1+u)^2+y2^2]^(1/2),r2=[(y1-v)^2+y2^2]^(1/2)


Rem 輸出坐標軸

Dim y1(2), y2(2)
T = 6.2
y1(1) = 1.2
y2(1) = 0
y3 = 0
y4 = -1.04936
u = 0.012129
v = 1 - u
h = InputBox("請輸入h:", "")
h = Val(h)
n = T / h

Cls
x0 = 7000
y0 = 5000
Line (200, y0)-(15000, y0)
Line (x0, 500)-(x0, 9000)

t0 = 2000


i = 2
Do While i <= n
   r1 = Sqr((y1(1) + u) * (y1(1) + u) + y2(1) * y2(1))
   r1 = r1 ^ 3
   r2 = Sqr((y1(1) - v) * (y1(1) - v) + y2(1) * y2(1))
   r2 = r2 ^ 3
   
   y1(2) = y1(1) + h * y3
   y2(2) = y2(1) + h * y4
   y3 = y3 + h * (y1(1) + 2 * y4 - v * (y1(1) + u) / r1 - u * (y1(1) - v) / r2)
   y4 = y4 + h * (y2(1) - 2 * y3 - v * y2(1) / r1 - u * y2(1) / r2)

   Line (x0 + y1(1) * t0, y0 - y2(1) * t0)-(x0 + y1(2) * t0, y0 - y2(2) * t0)
   
   y1(1) = y1(2)
   y2(1) = y2(2)

   i = i + 1
Loop


i = 1
Do While i <= n - 1
  i = i + 1
Loop

End Sub