vbnet求根的简单介绍

vb.net中Clnt(math.sqrt(math.P1^9))

File in = new File("C:\\input.sql");

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File out = new File("C:\\out.sql");

BufferedReader reader = null;

PrintWriter writer = null;

try {

reader = new BufferedReader(new FileReader(in));

writer = new PrintWriter(new FileOutputStream(out));

String text = null;

int line = 1;

while ((text = reader.readLine()) != null) {

writer.println(line + " " + text);

line++;

}

writer.flush();

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

} finally {

if (writer != null) {

writer.close();

}

if (reader != null) {

try {

reader.close();

} catch (IOException e) {

e.printStackTrace();

}

}

}

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）

========================

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

VB解方程

解一元一次方程：

设置4个文本框，分别代表一元一次方程中的参数k,b,x,y

分别命名txtk,txtb,txtx,txty.计算按钮命名为cmdCalc。

在代码窗口里粘贴如下代码:

Private Sub cmdCalc_Click()

Dim k, b As Long

k = txtk.Text

b = txtb.Text

If txtx.Text = "x" Then

MsgBox "x的值为:" (txty.Text - b) / k

ElseIf txty.Text = "y" Then

MsgBox "y的值为:" k * txtx.Text + b

End If

End Sub

计算时求x则在txtx那里输入一个x，

求y则在txty那里输入一个y，

在各文本框中输入参数，

然后按下按钮，

就有提示框弹出，显示结果。

一元二次方程：

privat sub command1_click()

dim a,b,c,x1,x2,d as sigle

a=val(textl.text)

b=val(text2.text)

c=val(text3.text)

d=b^2-4*a*c

if d0 then

x1=(-b+sqr(d))/(2*a)

x2=(-b-sqr(d))/(2*a)

else if d=0 then

x1=(-b/2*a)

x2=x1

else msgbox"方程没有实根"

end if

text4.text="x1=" x1 "" "x2=" x2

end sub

sub min(byref a() as integer)

dim i,j as interger

for i=1 to 9

for j=i+1 to 10

if a a(i)a(j) then

t=a(j)

a(i)=a(j)

a(j)=t

end if

next

next

end sub

private sub command_(click)

dim b(1 to 10) as interger

dim a(1 to 10) as interger

randomize

for i=1 to 10

a(i)=int(rnd*90)+10

list1.additem a(i)

b(i)=int(rnd*90)+ 10

list2.additem b(i)

next

call min(a)

call min(b)

if a(1)b(1) then

m=a(1)

else

m=b(1)

end if

text1.text="A,B种的最小值：" vbcrlf m

end sub

一元三次方程：

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）

========================

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

二元一次方程：

Dim a, b, c As Integer

Dim x, y As Single

Dim d As Double

a = Val(InputBox("输入二次项系数"))

b = Val(InputBox("输入一次项系数"))

c = Val(InputBox("输入常数项"))

d = b ^ 2 - 4 * a * c

If d 0 Then

MsgBox "方程无解"

ElseIf d = 0 Then

x = -b / (2 * a)

MsgBox "方程有一个解：" x

Else

x = (-b + Sqr(d)) / (2 * a)

y = (-b - Sqr(d)) / (2 * a)

MsgBox "方程有两个解：" x "和" y

End If

三元一次方程：

方程组如下,

ax+by+cz=d

a'x+b'y+c'z=d'

a"x+b"y+c"z=d"

其中x,y,z为未知数,a,a',a",b,b',b",c,c',c",d,d',d",为用户输入的数值

解N元一次方程，indat为N+1行、N列的数组，outdat为N个元素的数组

Public Sub 解方程(ByRef InDat() As Double, ByVal InDatCount As Long, ByRef OutDat() As Double, ByRef OutDatCount As Long)

Dim Xt() As Double

Dim Dt As Double

Dim Ss As Long

Dim OtSCount As Long

Dim XtOut() As Double

If InDatCount 1 Then

ReDim Xt(1 To InDatCount - 1, 1 To InDatCount) As Double

For j = 1 To InDatCount - 1 '行

For i = 2 To InDatCount + 1 '列

Xt(j, i - 1) = InDat(j, i) * InDat(InDatCount, 1) / InDat(1, 1) - InDat(InDatCount, i)

Next i

Next j

OtSCount = 0

解方程 Xt, InDatCount - 1, XtOut, OtSCount

Dt = 0

For i = 1 To InDatCount - 1

Dt = Dt + InDat(InDatCount, i + 1) * XtOut(i)

Next i

Dt = Dt + InDat(InDatCount, i + 1)

ReDim Preserve OutDat(1 To 1 + OtSCount) As Double

OutDat(1) = -Dt / InDat(InDatCount, 1)

For i = 2 To OtSCount + 1

OutDat(i) = XtOut(i - 1)

Next i

OutDatCount = 1 + OtSCount

Else

ReDim OutDat(1 To 1) As Double

If InDat(1, 1) 0 Then

OutDat(1) = -InDat(1, 2) / InDat(1, 1)

Else

OutDat(1) = 0

End If

OutDatCount = 1

End If

End Sub

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“|”，可以直接显示，同理对数可用log(x)代替，根号和其他不支持显示。

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。

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)

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