VB 牛顿迭代法、二分法和弦截法解一元三次方程.doc

VB 牛顿迭代法、二分法和弦截法解一元三次方程Option ExplicitPrivate a As Double, b As Double, c As Double, d As Double, xx1 As Double, xx2 As Double, e As DoublePrivate 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 SubPrivate 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) 0 And y2 0) Or (y1 0 And y2 0) Then Print y1= & y1 & y2= & y2 & ，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 = & x1 Print 迭代次数 i = & i ElseIf y2 = 0 Then Print 二分法 x = & x2 Print 迭代次数 i = & i Else For i = 1 To 1000 x0 = (x1 + x2) / 2 Debug.Print x0 y0 = f(a, b, c, d, x0) If y0 = 0 Then Print 二分法 x = & x0 Print 迭代次数 i = & i Print Exit Sub ElseIf Abs(x1 - x2) e Then Print 二分法 x = & x0 Print 迭代次数 i = & i Print Exit Sub ElseIf (y1 0 And y0 0 And y0 0) Then x1 = x0 Else x2 = x0 End If Next Print 失败! End If PrintEnd SubPrivate 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 y1= & y1 & y2= & y2 & ，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 = & x1 Print 迭代次数 i = & i ElseIf y2 = 0 Then Print 弦截法 x = & x2 Print 迭代次数 i = & i Else For i = 1 To 1000 x0 = x1 - (x2 - x1) / (y2 - y1) * y1 Debug.Print x0 y0 = f(a, b, c, d, x0) If y0 = 0 Then Print 弦截法 x = & x0 Print 迭代次数 i = & i Print Exit Sub ElseIf Abs(x1 - x2) e Then Print 弦截法 x = & x0 Print 迭代次数 i = & i Print Exit Sub ElseIf (y1 0 And y0 0 And y0 0) Then x1 = x0 Else x2 = x0 End If Next Print 失败! End If PrintEnd SubFunction 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 + dEnd FunctionFunction f1(a As D