little help with this VB program???

[acejj26]

I am writing a numerical analysis program, and i am working on Bisection method. I am writing it in VB because I am pretty comfortable with it. However, I cannot seem to figure out how to bring in a text string that contains the function at hand and then manipulate it so I can use the bisection method to figure the root. Below is my code so far. I would appreciate any help.

Option Explicit

Dim Tolerance As Double
Dim a As Double
Dim b As Double
Dim Max As Double
Dim root As Double
Dim funct As String
Dim x As Double
Dim p As Double
Dim i As Integer
Dim z As Integer
Dim f As Double
Dim result_a As Double
Dim result_p As Double
Dim result As Double
Dim newfunct As String
Dim val_funct As Double

Public Sub cmdRoot_Click()

funct = txtFunction.Text
a = txtEndA.Text
b = txtEndB.Text
Tolerance = txtTOL.Text
Max = Int(txtIterations.Text)

i = 1

result_a = eval(a, funct)

Do While i <= Max

p = a + ((b - a) / 2)

result_p = eval(p, funct)

If result_p = 0 Then

lblMessage.Caption = &quot;Procedure completed successfully. The root is at x = &quot; &amp; Str(p)
Exit Do


End If

If ((b - a) / 2) < Tolerance Then

lblMessage.Caption = &quot;Procedure completed successfully. The root is at x = &quot; &amp; Str(p)
Exit Do

End If

i = i + 1

If (result_a * result_p) > 0 Then
a = p
result_a = result_p
Else
b = p
End If

Loop

End Sub

Private Function eval(ByVal f As Double, ByRef funct As String) As Double

newfunct = Empty

For z = 1 To Len(funct)

If Mid(funct, z, 1) = &quot;x&quot; Then
newfunct = newfunct &amp; Trim(Str(f))
Else
newfunct = newfunct &amp; Mid(funct, z, 1)
End If

Next z

val_funct = Val(newfunct)

End Function

Note that this has been edited from original form to include suggestions.

 

[acejj26]

bump

 

[Descartes]

I don't quite understand what you're saying. You want to manipulate a function based on a string variable that's an argument to the function? Hmm... welp...

1) VB doesn't have pointers, which is what you'd need to establish dynamically at run-time which function to execute based on a value supplied in a function call. You have a few options: you could implement a callback function in C/C++ (which can handle function pointers) and send in the name of your function using the AddressOf operator, or you could create a class module and pass it in ByVal to your function then call the appropriate method of the class. Both of these allow dynamic execution of functions at run-time based on whatever conditions you provide.

HTH at least a little.