Hi I'm completely new to using VB in excel, but could someone help me fix my program. I'm supposed to find the roots of the equation denoted as func using the newton raphson method. Currently I am not getting the correct roots and the range of values which can be input are very limited. Could someone help on how to fix this? Thanks!

Option Explicit
Function newton(guess)

Dim func As Double, deriv As Double, i As Double, x2 As Double, x As Double, dif As Double

x = guess

For i = 0 To 1000
    func = x ^ 2 * Sin(x) + x ^ 3 * Exp(x) - x * Cos(x) - 7
    deriv = (x ^ 2 - 1) * Cos(x) + 3 * x * Sin(x) + (x ^ 3 + 3 * x ^ 2) * Exp(x)
    x2 = (x - func) / deriv
    dif = x2 - x
    x = x2
    If Abs(dif) < 0.001 Then i = 1000
Next i

newton = x
    
End Function

what is the use of the for loop ?

That's old school Basic. For i = 0 to 1000 is telling the proggie to start counting at 0 and stop at 1000. The func... statement has the proggie calculating each number it sees. Next i is telling the proggie move forward to the next number in the sequence....

(i.e., Start counting at 0, perform calculations, move on to next number (1,2,3,4,5...1000) )

Since 'for' is 0 to 1000 - it automatically stops at 1000.

...at least that's what it used to mean on the 'Trash 80's' (Radio Shack TRS-80 Microcomputer - w/ or w/o monitor)

...yea... i know... I just dated mahsef...

:cool:

Hi I'm completely new to using VB in excel, but could someone help me fix my program. I'm supposed to find the roots of the equation denoted as func using the newton raphson method. Currently I am not getting the correct roots and the range of values which can be input are very limited. Could someone help on how to fix this? Thanks!

Option Explicit
Function newton(guess)

Dim func As Double, deriv As Double, i As Double, x2 As Double, x As Double, dif As Double

x = guess

For i = 0 To 1000
    func = x ^ 2 * Sin(x) + x ^ 3 * Exp(x) - x * Cos(x) - 7
    deriv = (x ^ 2 - 1) * Cos(x) + 3 * x * Sin(x) + (x ^ 3 + 3 * x ^ 2) * Exp(x)
    x2 = (x - func) / deriv
    dif = x2 - x
    x = x2
    If Abs(dif) < 0.001 Then i = 1000
Next i

newton = x
    
End Function

I'm new too - so if I'm wrong, i apologize now...

First off, are you using VBA? (Visual Basic for Applications) - I've read that there are some inherent differences between it and 'regular' VB...

That being said, and here's where my math fails me, when calculating Sin and Cos - is it written as Sin(#) / Cos(#)?

Standard math says that x(y) = multiplication - so, are the numbers being multiplied by accident?

*scratches head*

If I'm not mistaken, you'd have to specify PI in a program (pi=3.14) - so would the same hold true for Sin & Cos...prior to your calculations? :?:

ur logic is wrong..............i cant say bout the code ,but newton ralphson method............u ar using has the wrong logic..

x2=x-(func/deriv)
this is the actual logic of newton ralphson method.

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