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vb..net求根函数 编写一个vb程序求方程的根
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如何用VB对”一元三次方程求根”问题进行编程
针对方程"ax^3+bx^2+cx+d=0"的求根程序。
控件只需一个Command1，结果显示在“立即”中。
代码如下。（参考）
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Private Sub Command1_Click()
Dim x1r As Double, x1i As Double, x2r As Double, x2i As Double, x3r As Double, x3i As Double
Dim ret As String
Const eq = "ax^3+bx^2+cx+d=0"
a = InputBox("请输入a", eq)
b = InputBox("请输入b", eq)
c = InputBox("请输入c", eq)
d = InputBox("请输入d", eq)
ret = CubicEquation(a, b, c, d, x1r, x1i, x2r, x2i, x3r, x3i) '5x^3+4x^2+3x-12=0
Debug.Print "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" ret
Debug.Print x1r; " + "; x1i; " i"
Debug.Print x2r; " + "; x2i; " i"
Debug.Print x3r; " + "; x3i; " i"
End Sub
Private Function CubicEquation _
(ByVal a As Double, ByVal b As Double, ByVal c As Double, ByVal d As Double, _
x1r As Double, x1i As Double, x2r As Double, x2i As Double, x3r As Double, x3i As Double) As String
'Cubic equation(v2.2), coded by btef (please let this line remain)
Dim e As Double, f As Double, g As Double, h As Double, delta As Double
Dim r As Double, sita As Double, pi As Double, rr As Double, ri As Double
If a = 0 Then
CubicEquation = "Not a cubic equation: a = 0"
Exit Function
End If
'pi = 3.14159265358979
pi = 4 * Atn(1)
b = b / a 'simplify to a=1: x^3+bx^2+cx+d=0
c = c / a
d = d / a
e = -b ^ 2 / 3 + c 'substitute x=y-b/3: y^3+ey+f=0
f = (2 * b ^ 2 - 9 * c) * b / 27 + d
If e = 0 And f = 0 Then
x1r = -b / 3
x2r = x1r
x3r = x1r
CubicEquation = "3 same real roots:"
ElseIf e = 0 Then 'need to deal with e = 0, or it will cause z = 0 later.
r = -f 'y^3+f=0, y^3=-f
r = Cur(r)
x1r = r - b / 3 'a real root
If r 0 Then 'r never = 0 since g=f/2, f never = 0 there
sita = 2 * pi / 3
x2r = r * Cos(sita) - b / 3
x2i = r * Sin(sita)
Else
sita = pi / 3
x2r = -r * Cos(sita) - b / 3
x2i = -r * Sin(sita)
End If
x3r = x2r
x3i = -x2i
CubicEquation = "1 real root and 2 image roots:"
Else 'substitute y=z-e/3/z: (z^3)^2+fz^3-(e/3)^3=0, z^3=-g+sqr(delta)
g = f / 2 '-q-sqr(delta) is ignored
h = e / 3
delta = g ^ 2 + h ^ 3
If delta 0 Then
r = Sqr(g ^ 2 - delta)
sita = Argument(-g, Sqr(-delta)) 'z^3=r(con(sita)+isin(sita))
r = Cur(r)
rr = r - h / r
sita = sita / 3 'z1=r(cos(sita)+isin(sita))
x1r = rr * Cos(sita) - b / 3 'y1=(r-h/r)cos(sita)+i(r+h/r)sin(sita), x1=y1-b/3
sita = sita + 2 * pi / 3 'no image part since r+h/r = 0
x2r = rr * Cos(sita) - b / 3
sita = sita + 2 * pi / 3
x3r = rr * Cos(sita) - b / 3
CubicEquation = "3 real roots:"
Else 'delta = 0
r = -g + Sqr(delta)
r = Cur(r)
rr = r - h / r
ri = r + h / r
If ri = 0 Then
CubicEquation = "3 real roots:"
Else
CubicEquation = "1 real root and 2 image roots:"
End If
x1r = rr - b / 3 'a real root
If r 0 Then 'r never = 0 since g=f/2, f never = 0 there
sita = 2 * pi / 3
x2r = rr * Cos(sita) - b / 3
x2i = ri * Sin(sita)
Else 'r 0
sita = pi / 3
x2r = -rr * Cos(sita) - b / 3
x2i = -ri * Sin(sita)
End If
x3r = x2r
x3i = -x2i
End If
End If
End Function
Private Function Cur(v As Double) As Double
If v 0 Then
Cur = -(-v) ^ (1 / 3)
Else
Cur = v ^ (1 / 3)
End If
End Function
Private Function Argument(a As Double, b As Double) As Double
Dim sita As Double, pi As Double
'pi = 3.14159265358979
pi = 4 * Atn(1)
If a = 0 Then
If b = 0 Then
Argument = pi / 2
Else
Argument = -pi / 2
End If
Else
sita = Atn(Abs(b / a))
If a 0 Then
If b = 0 Then
Argument = sita
Else
Argument = -sita
End If
ElseIf a 0 Then
If b = 0 Then
Argument = pi - sita
Else
Argument = pi + sita
End If
End If
End If
End Function
相关问答
Q1: VB.net的开方运算
VB的运算顺序是：先乘除、后加减，有括号的先算括号内，有负号的先算负号。
请你比较一下这个运算中x和y的值：
Dim n As Single = 4
Dim x As Single
Dim y As Single
x = n + 1
x = x / n
x = x - 1
x = Math.Sqrt(x)
y = Math.Sqrt((n + 1) / n - 1)
这样就会发现，你的代码中括号的位置错了。
正确的应该是： Math.Sqrt((n + 1) / n - 1)
Q2: vb常用的数学函数中立方根的函数名是什么
立方根函数名vb..net求根函数：^运算符
用来求一个数字vb..net求根函数的某次方vb..net求根函数，次方数为 exponent 值
debug.Print 5^(1/3)
1.7099759466767
上面代码是取5的立方根的代码演示。
Q3: vb.net 编写一个函数
注意：参数为动态数组；
Private Function MyF(ByRef d() As Integer)
ReDim d(4, 13) As Integer
Dim i As Integer
Dim j As Integer
Dim n As Integer
Dim MyNum(4) As Integer
For i = 1 To 4
MyNum(i) = 0
Next i
Randomize
For i = 1 To 4
For j = 1 To 13
n = Int(Rnd * 4 + 1)
Do While MyNum(n) = 13
n = Int(Rnd * 4 + 1)
Loop
d(i, j) = n
MyNum(n) = MyNum(n) + 1
Next j
Next i
End Function
Q4: Sqrt()在VB里怎么使用？
在VB6中，没有名为Sqrt（）函数或子过程；只有Math.Sqr(...)函数！
函数 Math.Sqr(x)求一个数x的平方根。这个函数中
x≥0
所得结果（根）为Double类型
举例如下：
Dim root As Double
root = Math.Sqr(10)
MsgBox "10的平方根为：" + CStr(root)
如果试图求一个负数的平方根引发错误：
Q5: VB.NET 如何绘制数学代数式（公式、方程、函数解析式等）？
绝对值是“|”vb..net求根函数，可以直接显示，同理对数可用log(x)代替，根号和其vb..net求根函数他不支持显示。
如果要显示数学式子，只能画吧。
计算时可用“^”求幂或求根，“/”表示除法和分数线，还有math类。
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