VB 牛顿迭代法、二分法和弦截法解一元三次方程
今年的高考分数线-辞职书样本
VB 牛顿迭代法、二分法和弦截法解一元三次方程
Option
Explicit
Private a As Double, b As Double, c
As Double, d As Double, xx1 As Double, xx2 As
Double,
e As Double
Private Sub
Form_Load()
a = 1 'a * x ^
3 + b * x ^ 2 + c * x + d = 0
b = 2
c = 3
d = -4
xx1 = 0
'二分法区间或弦截法区间或牛顿迭代法初值
xx2 = 1
'二分法区间或弦截法区间
e = 0.00001 '精度
End Sub
Private Sub Command1_Click()
'牛顿迭代法
Dim x As Double, y As
Double, dy As Double, ydy As Double, i As Long
x = xx1
For i =
0 To 1000
y = f(a, b, c, d, x)
dy = f1(a, b, c, x)
If Abs(y) < e Then
Print 牛顿迭代法 x =
Print 迭代次数 i =
Print
Exit Sub
ElseIf dy = 0 Then
Print 失败，请另设初值试试
Print
Exit Sub
End If
ydy = y
dy
x = x - ydy
Next
Print 失败!
Print
End
Sub
Private Sub Command2_Click()
'二分法
Dim x1 As Double, x2 As
Double, x0 As Double, y1 As Double, y2 As Double,
y0 As
Double, i As Long
x1 =
xx1
x2 = xx2
y1 = f(a, b, c, d,
x1)
y2 = f(a, b, c, d, x2)
If (y1 > 0 And y2 > 0) Or (y1 < 0 And y2 < 0) Then
Print
，二分法里y1与y2不能同号，请重新设置x1和
x2
ElseIf y1 = 0
Then
Print 二分法 x =
Print
迭代次数 i =
ElseIf y2 = 0 Then
Print 二分法 x =
Print 迭代次数 i =
Else
For i = 1 To 1000
x0 = (x1 + x2) 2
' x0
y0 = f(a, b, c, d, x0)
If y0 = 0 Then
Print 二分法 x =
Print 迭代次数 i =
Print
Exit
Sub
ElseIf Abs(x1 - x2) < e Then
Print 二分法 x =
Print 迭代次数 i =
Print
Exit Sub
ElseIf (y1 < 0 And y0 <
0) Or (y1 > 0 And y0 > 0) Then
x1 = x0
Else
x2 = x0
End If
Next
Print 失败!
End If
Print
End Sub
Private Sub Command3_Click() '弦截法
Dim x1 As Double, x2 As Double, x0 As
Double, y1 As Double, y2 As Double, y0 As
Double, i As Long
x1 = xx1
x2 = xx2
y1 = f(a, b, c, d, x1)
y2 = f(a, b, c, d, x2)
If
(y1 > 0 And y2 > 0) Or (y1 < 0 And y2 < 0) Then
Print
，二分法里y1与y2不能同号，请重新设置x1和
x2
ElseIf y1 = 0
Then
Print 弦截法 x =
Print
迭代次数 i =
ElseIf y2 = 0 Then
Print 弦截法 x =
Print 迭代次数 i =
Else
For i = 1 To 1000
x0 = x1 - (x2 - x1) (y2 - y1) *
y1
' x0
y0 = f(a,
b, c, d, x0)
If
y0 = 0 Then
Print 弦截法 x =
Print 迭代次数 i =
Print
Exit Sub
ElseIf Abs(x1 - x2) < e
Then
Print 弦截法 x =
Print 迭代次数 i =
Print
Exit Sub
ElseIf (y1 < 0 And y0 <
0) Or (y1 > 0 And y0 > 0) Then
x1 = x0
Else
x2 = x0
End If
Next
Print 失败!
End If
Print
End Sub
Function f(a As Double, b As Double, c As
Double, d As Double, x As Double) As Double
f = a * x ^ 3 + b * x ^ 2 + c * x + d
End Function
Function f1(a As Double, b As
Double, c As Double, x As Double) As Double
f1 = 3 * a * x ^ 2 + 2 * b * x + c
End Function