牛顿迭代法.frm

Visual Basic课程举例1 有很好的例题

VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "牛顿迭代法解一元方程"
   ClientHeight    =   6180
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   7095
   BeginProperty Font 
      Name            =   "Arial Black"
      Size            =   18
      Charset         =   0
      Weight          =   400
      Underline       =   0   'False
      Italic          =   0   'False
      Strikethrough   =   0   'False
   EndProperty
   LinkTopic       =   "Form1"
   Picture         =   "牛顿迭代法.frx":0000
   ScaleHeight     =   6180
   ScaleWidth      =   7095
   StartUpPosition =   3  '窗口缺省
   Begin VB.TextBox Text1 
      Height          =   615
      Left            =   3000
      TabIndex        =   1
      Text            =   "-2"
      Top             =   4200
      Width           =   1575
   End
   Begin VB.CommandButton Command1 
      Caption         =   "求根"
      BeginProperty Font 
         Name            =   "宋体"
         Size            =   15.75
         Charset         =   134
         Weight          =   700
         Underline       =   0   'False
         Italic          =   0   'False
         Strikethrough   =   0   'False
      EndProperty
      Height          =   615
      Left            =   4920
      TabIndex        =   0
      Top             =   5520
      Width           =   2175
   End
   Begin VB.Label Label1 
      BackStyle       =   0  'Transparent
      Caption         =   "输入初值"
      Height          =   495
      Left            =   2880
      TabIndex        =   2
      Top             =   3600
      Width           =   1575
   End
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
DefDbl F, X
Private Sub Command1_Click()
'牛顿迭代法求3x3-4x2-5x+3=0在x=3附近的一个实根
    X1 = Val(Text1)        '迭代初值
    I = 0
    Do
        I = I + 1
        x0 = X1   '为下一次迭代作准备
        fx = 3 * x0 ^ 3 - 4 * x0 ^ 2 - 5 * x0 + 3
        flx = 9 * x0 ^ 2 - 8 * x0 - 5
        X1 = x0 - fx / flx
    Loop While Abs(X1 - x0) > 0.0000000001
    Print "迭代次数:"; I; "x="; X1 '输出所求高次方程的根

End Sub