trouble with results of equation

[kokopeli]

I am having trouble with getting the proper results from an equation. I have simplified the equation for this example. The numbers on the left increment properly, but the results are wierd. The numbers on the right should two times the number on the left. ( in each column )

Option Explicit
'This code assumes a text box called Text1 set to multiline
'true and a command button named Command1
Private Sub Command1_Click()
Dim ResultsArray() As Single 'Or whatever
Dim g As Single
Dim r As Single
Dim l As Single
Dim h As Single
Dim v As Single
Dim TempStr As String

r = 20
ReDim ResultsArray(1 To 2 * r)
l = 72
For h = 1 To (2 * r) - 1 Step 0.5
v = h * 2
ResultsArray(h) = v
Next h
TempStr = ""
For h = 1 To r Step 0.5
TempStr = TempStr & h & Chr(9) & ResultsArray(h) & _
Chr(9) & Chr(9) & Chr(9) & _
h + r & Chr(9) & ResultsArray(h + r) & vbCrLf
Next h


Text1.Text = TempStr


End Sub

[seaweed]

I think the problem is that you aren't using whole numbers for your array indexes in the loops. I have never seen an array use singles as an index, and I don't think you can do that. (I could be wrong...?).

I changed your code using an integer variable for your array index, so now it works just fine (although I can't for the life of me figure out what the purpose is!).

Try this:

Option Explicit
'This code assumes a text box called Text1 set to multiline
'true and a command button named Command1
Private Sub Command1_Click()
    Dim ResultsArray() As Single
    Dim g As Single
    Dim r As Single
    Dim l As Single
    Dim h As Single
    Dim v As Single
    Dim TempStr As String
    Dim ArrayIndex As Integer
    
    r = 20
    TempStr = ""
    ArrayIndex = 1
    
    ReDim ResultsArray(1 To 4 * r)
    
    For h = 1 To (2 * r) Step 0.5
        v = h * 2
        ResultsArray(ArrayIndex) = v
        ArrayIndex = ArrayIndex + 1
    Next h
    
    ArrayIndex = 1
    
    For h = 1 To r Step 0.5
        TempStr = TempStr & h & Chr(9) & ResultsArray(ArrayIndex) & _
        Chr(9) & Chr(9) & Chr(9) & _
        h + r & Chr(9) & ResultsArray(ArrayIndex + r * 2) & vbCrLf
        ArrayIndex = ArrayIndex + 1
    Next h

    Text1.Text = TempStr
End Sub

Edited by seaweed on 03-10-2000 at 05:01 AM

[kokopeli]

Seaweed, if you are still out there I can explain. This is a program to measure the volume of liquid in a cylindrical tank, laying horizontally. In the code below I have commented out some of your code to show you what I mean. I guess I simplified my code too much on my first submission. Your code did exactly what I wanted on the simplified versiopn, but it wont work on the real code. This assumes Command1 and Text1 set to multiline. FYI: (L)variable is the length of the tank, (r) is the radius(explaining r*2) and (h) is the height in inches of liquid in the tank. (v) is the volume. It will work with one inch increments, but I would like to use a Step variable of 1, .5, at least and maybe .250. Option Explicit
Private Sub Command1_Click()
Dim ResultsArray() As Single 'Or whatever

Dim r As Single
Dim L As Single
Dim h As Single
Dim v As Single
Dim TempStr As String
Dim Title As String
Dim ArrayIndex As Integer
'then when you need to use the arrays:

r = 20
TempStr = ""
'ArrayIndex = 1

ReDim ResultsArray(1 To 4 * r)

L = 72

For h = 1 To (2 * r) - 1 'Step 0.5
v = (r ^ 2 * (ArcCos((r - h) / r))) _
- (r - h) * (Sqr(2 * (r * h) - h ^ 2))
v = l * v / 231
v = Format(v, "######.##")
ResultsArray(h) = v
'ArrayIndex = ArrayIndex + 1

Next h

'ArrayIndex = 1

For h = 1 To r 'Step 0.5
TempStr = TempStr & h & Chr(9) & ResultsArray(h) & _
Chr(9) & Chr(9) & Chr(9) & _
h + r & Chr(9) & ResultsArray(h + r) & vbCrLf
Next h

Title = "This is a test"
Text1.Text = Title & vbCrLf & TempStr


End Sub

'Inverse Cosine
Function ArcCos(x As Double) As Double
ArcCos = Atn(-x / Sqr(-x * x + 1)) + 2 * Atn(1)
End Function

[kokopeli]

Does anyone know how to do this?

[seaweed]

From what I can tell, you are still going to run into the same problem of using a single as an array index.

Now, if the commented code that you last posted returns correct results, then we can infer that if the Step value is 1, then the upper bound of the array is 4 * r from this line of code:

ReDim ResultsArray(1 To 4 * r)

We also know that if you change the step value to 0.5, that the number of elements in the array will double. If you change the step to 0.25, the number of elements will quadruple. This leads into a formula, 1/StepValue. If the step value is .5 then 1/.5 = 2 (doubling the array size), and if it's .25 then 1/.25 = 4 (quadrupling the array size). Therefore, you can use the following formula to calculate the upper bound of the array:

UpperBound = (1 / StepValue) * 4 * r

What I did is in the Form_Load, ask the user what the step value will be and hold that value in a global variable (Increment). Then just plug that value into the formula and it should work. Try the following and see if you get the correct results:

Option Explicit

Private Increment As Single   'This holds the step increment

Private Sub Form_Load()
    'Step increment is assigned here. You could put this in a
    'command button also, if you wanted to try different
    'increments without starting and stoping your project each time
    
    Me.Show
    On Error Resume Next    'In case user clicks cancel
    Increment = CSng(InputBox("What increment do you want to use?"))
    If Increment <= 0 Then
        Increment = 1
    End If
End Sub

Private Sub Command1_Click()
    Dim ResultsArray() As Single
    Dim Radius As Single
    Dim Length As Single
    Dim Height As Single
    Dim Volume As Single
    Dim TempStr As String
    Dim Title As String
    Dim ArrayIndex As Integer
    
    Radius = 20
    Length = 72
    TempStr = ""
    ArrayIndex = 1
    
    ReDim ResultsArray(1 To (1 / Increment) * 4 * Radius)
        
    For Height = 1 To (2 * Radius) - 1 Step Increment
        Volume = Format(Length * ((Radius ^ 2 * (ArcCos((Radius - Height) / _
            Radius))) - (Radius - Height) * (Sqr(2 * (Radius * Height) - _
            Height ^ 2))) / 231, "######.##")
        ResultsArray(ArrayIndex) = Volume
        ArrayIndex = ArrayIndex + 1
    Next Height
    
    ArrayIndex = 1
    
    For Height = 1 To Radius Step Increment
        TempStr = TempStr & Height & Chr(9) & ResultsArray(ArrayIndex) & _
        Chr(9) & Chr(9) & Chr(9) & _
        Height + Radius & Chr(9) & ResultsArray(ArrayIndex + ((1 / Increment) _
            * Radius)) & vbCrLf
        ArrayIndex = ArrayIndex + 1
    Next Height
    
    Title = "This is a test"
    Text1.Text = Title & vbCrLf & TempStr

End Sub

Function ArcCos(x As Double) As Double
    ArcCos = Atn(-x / Sqr(-x * x + 1)) + 2 * Atn(1)
End Function

Let me know if this doesn't work! We'll keep plugging away at it.

~seaweed