how to calculate the number of looping?

[vbwire]

i use vb 6.0

 
Option Explicit
 
Dim Error As Double
Dim x As Integer
Dim y As Double
Dim z As Integer
Dim eps As Double
Dim N As Integer
 
Private Sub cmdCalculate_Click()
 
'user input
 
If IsNumeric(txtN) And IsNumeric(txtEps) And IsNumeric(txtX) Then
N = txtN.Text
eps = txtEps.Text
x = txtX.Text
Else
    MsgBox "all input must be numeric", vbExclamation, "numeric test"
    txtN.SetFocus
End If
 
'calculate
 
Do
    y = (x) - (x - (N ^ (1 / 2)))
 
    Error = y - x
    If Error < 0 Then
        Error = Error * -1
    End If
 
  z = z + 1
 
Loop Until Error < eps
 
'display the result
lblDisplay.Caption = "root : " & y & "  iteration : " & z
 
 
 
End Sub
 
Private Sub cmdExit_Click()
Unload Me
End Sub
 

the problems..

the 'eps' is the decimal places.in my program above it need user to insert the number of decimal places like this '0.001'.. but actually i just want the user put the value as '3'...

the iteration value must be in integer data type as the result of number of looping it takes to complete the loop.. the number of looping (iteration) didn't match its actually value..

[Stewart Ross]

Hi vbwire. It would be helpful to know what the loop calculation is for. When I test it the calculated error value remains constant and the loop does not exit.

I wonder if your reference to root N (N ^ (1/2)) in the loop is correct? N is not changing after it is entered by the user, and I guess there should a use of the loop counter z somewhere to change the value of N if the iterative calculation is intended to reduce the error value below the loop threshold. This is just a guess, though.

To refer to the number of decimal places for the loop threshold as an integer value you could define a variable NDecimals as an integer, get the value of NDecimals from the user instead of the double eps, then replace your loop exit test with

Loop Until Error < 10^(-NDecimals)

Another change is to use the Abs (absolute value) function to replace

Error = y - x
If Error < 0 Then 
Error = Error * -1
End If

with

Error = abs(y-x)

Regards

Stewart

[Killer42]

As far as I could see, z should correctly return the number of iterations.

As for the calculation, I haven't looked into it in detail. But if you have any Integer data types in there, VB may convert interim results to Integer, thus losing precision. Try using all Double data types in there. And that includes for the literal values. If you say "1#" instead of just "1", you will force VB to use double data type for the value. In any case, why use (1/2), when you could just use the actual value, 0.5?

Oh, one other thing. Between lines 20 and 21, I believe you should Exit Sub.

[vbwire]

Hi vbwire. It would be helpful to know what the loop calculation is for. When I test it the calculated error value remains constant and the loop does not exit.

the loop calculate the value for y until the different between y and x is smaller than 'eps' ..

z is the number of looping it takes to complete the loop..

the value of x will take the value of y for the next looping.. for example in the first looping, x=2, then get the value of y.. then it will loop,use the value of y we get to calculate the new y. its continue give a new y until the different of the new y and y before it smaller than 'eps'

[MikeTheBike]

the loop calculate the value for y until the different between y and x is smaller than 'eps' ..

z is the number of looping it takes to complete the loop..

the value of x will take the value of y for the next looping.. for example in the first looping, x=2, then get the value of y.. then it will loop,use the value of y we get to calculate the new y. its continue give a new y until the different of the new y and y before it smaller than 'eps'

Hi
I started to look at this yesterday, but work got in the way (such a pain!).

Apart from the use of Abs() and changing the loop exit condition to

Loop Until Error < 0.1 ^ eps

there does not seem to be any iteration in the loop, ie. nothing changes from one loop to the next! So I've moded the code as follows:-

Option Explicit
 
Dim Error As Double
'Dim x As integer
Dim x As Double
Dim y As Double
Dim z As Integer
Dim eps As Double
Dim N As Integer
 
Private Sub cmdCalculate_Click()
 
    Dim txtX As Integer
    'Dim txtY As Double
    Dim txtZ As Integer
    Dim txtN As Integer
    Dim txtEps As Integer
 
 
'user input
    txtX = 3
    txtZ = 5
    txtN = 1000
    txtEps = 3
 
    z = 0
    If IsNumeric(txtN) And IsNumeric(txtEps) And IsNumeric(txtX) Then
    N = txtN
    eps = txtEps
    x = txtX
    Else
        MsgBox "all input must be numeric", vbExclamation, "numeric test"
        'txtN.SetFocus
        Exit Sub
    End If
 
    'calculate
 
    Do
        y = (x) - (x - (N ^ (1 / 2)))
 
        Error = Abs(y - x)
        x = y
        z = z + 1
 
    Loop Until Error < 0.1 ^ eps
 
    'display the result
    'lblDisplay.Caption = "root : " & y & "  iteration : " & z
    MsgBox "root : " & y & "  iteration : " & z
 
End Sub

ie have added x=y in the loop (as you indicted in the last post), but this always calculated the squre root of N in 2 iterations !!??

I still don't know what you are trying to do ?

Is this homework ?

ps. as this is not written in a form module I've hard coded values of txtN etc.



MTB

[vbwire]

thank to both of you..

this is the program after i corrected it..

Option Explicit
 
Dim Error As Double
Dim x As Double
Dim y As Double
Dim z As Integer
Dim eps As Double
Dim a As Integer
Dim N As Integer
 
Private Sub cmdCalculate_Click()
 
'user input
 
If IsNumeric(txtN) And IsNumeric(txtEps) And IsNumeric(txtX) Then
N = txtN.Text
a = txtEps.Text
x = txtX.Text
Else
    MsgBox "all input must be numeric", vbExclamation, "numeric test"
    txtN.SetFocus
End If
 
'calculate
 
eps = (10 ^ (-a))
 
Do
    y = x - (x - (N ^ (1 / 3)))
 
    Error = Abs(y - x)
 
    x = y
 
    z = z + 1
 
Loop Until Error < eps
 
'display the result
lblDisplay.Caption = "root : " & y & "             iteration : " & z
 
End Sub
 
Private Sub cmdExit_Click()
Unload Me
End Sub
 
 

please look at my code for displaying the result.. how to make it in two line but i want it in same label.

also.. i want to display the result for root in the decimal palaces chosen by user,'eps'..

[vbwire]

ie have added x=y in the loop (as you indicted in the last post), but this always calculated the squre root of N in 2 iterations !!??

I still don't know what you are trying to do ?

Is this homework ?

ps. as this is not written in a form module I've hard coded values of txtN etc.



MTB

thank you mike.. =)

i just realise my mistake in the calculation..

y = (x) - (x - (N ^ (1 / 2)))
 

its actually..

y = x - (x - (N ^ (1 / 3)))
 

and check my previous post.. i still have something for you..haha..