Polynommial calculator

[MOORPHEEUUS]

Can someone please tell me IF IT´S POSSIBLE, to have a vba code for calculating real-valued root of the polynomial of n power in excel 2007, by using Newton method?
i tried to solve a simple P(x) such as X^10 + X^9+X^8+X^7+X^6 +X^5+X^4+X^3+X^ 2+X-200 = 0 , by using solver from excel 2007, but it didn't work out.
Al old friend of mine, NEO, send me the following code:

Sub polySolver(coeffs As Range, powers As Range) As Double 
    Dim rowCount As Integer 
    Dim i 
    Dim iii 
    Dim xn As Double 
    Dim xnm1 As Double 
    Dim fx As Double 
    fx = 0 
    Dim fxprime As Double 
    fxprime = 0 
    xnm1 = 0.1 
    Do 
        For Each i In coeffs 
            For Each iii In powers 
                fx = (fx + i) * xnm1 ^ iii 
                fxprime = fxprime + (iii * i) * xnm1 ^ (iii - 1) 
                 
                xn = xnm1 - fx / fxprime 
                xnm1 = xn 
                 
            Next i 
        Next iii 
    Loop Until (Abs(fx) < 0.00001) 
     
    polySolver = xn 
End Function

but i haven't any sucess with it in trying to find root (s)of P(x) above ..
Can someone help fix it up??
I'm looking forward to receiving good news.
many thks

[Honduras2811]

This looks interesting. I'll see what I can do with it.

After a very quick look there are some serious problems with your code. Did it run at all? If so, I'm surprised.

1. PolySolver should be declared as a Function, not a Subroutine. Returning a value makes it a function.

2. Haphazard use of parentheses. Parentheses determine the order of execution of mathematical functions. Never be afraid to use too many parentheses, both to make life easier for the computer and for you. I've never seen the actual algorithm but it would be a miracle if the mathematical expressions return anything meaningful the way they are.

For instance in this line:

fxprime = fxprime + (iii * i) * xnm1 ^ (iii - 1)

Due to the precedence of mathematical operators the computer will do this, I think:

1. Raise xnm1 to the (iii - 1) power
2. multiply (iii * i)
3. multiply the result of 2. by the new value of xnml
4. Add the result to fxprime
5. Assign the result to fxprime.

Is that what you want it to do?

[Honduras2811]

OK. I got it to compile with no errors. It produces 0s, but it does it very quickly.[

I converted it to VB 6 because I haven't used VBA for a decade. If you have any questions about the changes I made, just ask.

Here's the modified code.

Option Explicit

'---------------------------------------------------------
' Procedure : cmdRun_Click
' Author    : Rory Starkweather
' Date      : 04/07/2014
' Purpose   : Fill two arrays that replace the Range type
'               variables that Excel VBA uses. intCoeffs is
'               filled with 10 1s. intPowers is filled donward
'               from 10 to 1. This matches up with the example
'               in the OP.
'---------------------------------------------------------
Private Sub cmdRun_Click()

    Dim intCoeffs(1 To 10) As Integer
    Dim intPowers(1 To 10) As Integer
    Dim intIndex As Integer
    Dim dblResult As Double
    
    On Error GoTo cmdRun_Click_Error
      Dim errstrErrorMessage As String
      Dim errlngRetVal As Long

    For intIndex = 10 To 1 Step -1
        intCoeffs(intIndex) = 1
        intPowers(intIndex) = intIndex
    Next ' intIndex
    
    dblResult = rsPolySolver(intCoeffs(), intPowers())
    frmMain.lblRoot.Caption = CStr(dblResult)

    '*** On Error GoTo 0
    Exit Sub

cmdRun_Click_Error:

    errstrErrorMessage = "Error " & Err.Number & _
                         " (" & Err.Description & _
                         ") in procedure cmdRun_Click" & _
                         " of Form frmMain"
    errlngRetVal = MsgBox(errstrErrorMessage, _    vbExclamation + vbOKOnly)
    
End Sub

Option Explicit

'///Public Function PolySolver(coeffs As Range, powers As Range) As Double
'---------------------------------------------------------------------------------------
' Procedure : rsPolySolver
' Author    : Rory Starkweather
' Date      : 04/07/2014
' Purpose   : The good stuff. Almost. Only the looping code was changed. The
'              math is exactly like the original.
'---------------------------------------------------------------------------------------
Public Function rsPolySolver(ByRef intCoeffs() As Integer, _
                            ByRef intPowers() As Integer) As Double

    'Dim rowCount As Integer    *Not used
    Dim i As Integer
    Dim iii As Integer
    Dim xn As Double
    Dim xnm1 As Double
    Dim fx As Double
    Dim fxprime As Double
    
    Dim intInnerIndex As Integer
    Dim intOuterIndex As Integer
    
    On Error GoTo PolySolver_Error
      Dim errstrErrorMessage As String
      Dim errlngRetVal As Long

    fx = 0
    fxprime = 0
    xnm1 = 0.1
    
    
    Do
        '///For Each i In coeffs
        For intOuterIndex = 1 To 10
            i = intCoeffs(intOuterIndex)
            '///For Each iii In powers
            For intInnerIndex = 1 To 10
                iii = intPowers(intInnerIndex)
                fx = (fx + i) * xnm1 ^ iii
                fxprime = fxprime + (iii * i) * xnm1 ^ (iii - 1)
 
                xn = xnm1 - fx / fxprime
                xnm1 = xn
 
            '///Next i
            Next ' intInnerIndex
        '///Next iii
        Next ' intOuterIndex
        
    Loop Until (Abs(fx) < 0.00001)
 
    rsPolySolver = xn

    '*** On Error GoTo 0
    Exit Function

PolySolver_Error:

    errstrErrorMessage = "Error " & Err.Number & _
                         " (" & Err.Description & _
                         ") in procedure PolySolver" & _
                         " of Module mdlProcs"
    errlngRetVal = MsgBox(errstrErrorMessage, vbExclamation + vbOKOnly)

    
End Function

It exits the Loop the first time Abs(fx)is tested because fx is always 0.