Question

First off, here is what I have so far:

Option Explicit

Dim y As Variant
Dim yforx As Variant
Dim yfork As Variant
Dim ynew As Variant
Dim ymin As Variant
Dim x As Variant
Dim xmin As Variant
Dim k As Variant
Dim kmin As Variant
Dim s As Variant
Dim Z As Variant
Dim Track As Variant


Sub PracticeProgram()

'Selects the right sheet
Sheets("PracticeProgram").Select

'y = k ^ 2 * (x ^ 2 + 2 * x * k - 6) / (x + k) ^ 2

'these are the bounds we are stepping through
Track = 0
x = 1
xmin = 1
k = 1
kmin = 1
y = 100000000
yforx = 100000
yfork = 1000000000

Do
    y = 100000000
    For x = 0 To 1000 Step 0.1
        ynew = kmin ^ 2 * (x ^ 2 + 2 * x * kmin - 6) / (x + kmin) ^ 2

        'This checks the new y-value against an absurdly high y-value we know is wrong. if it is less than this y-value, we keep the x-value that corresponds with it.
        If ynew < y Then
            xmin = x
            y = ynew
            yforx = y
            xmin = Application.Evaluate("=Round(" & xmin & ", 3)")
        Else
        End If

    Next
  MsgBox (yforx)


    For k = 0 To 1000 Step 0.1
        y = k ^ 2 * (xmin ^ 2 + 2 * xmin * k - 6) / (xmin + k) ^ 2
        If ynew < y Then
            kmin = k
            y = ynew
            yfork = y
            kmin = Application.Evaluate("=Round(" & kmin & ",3)")
        Else
        End If
        Next

    MsgBox (yfork)

Loop Until (Abs(yforx - yfork) < 10)

End Sub

This program is supposed to find the values of x and k in order to minimize the value of y. This is a practice for a much more complicated program that will use this same concept. In my actual program y, k, and x will all be greater than zero no matter what, but since it was hard to think of a simple equation whose results would be in the shape of a parabola opening up, I decided to allow negative answers for this practice program.

Basically, it should bounce back and forth between the equations finding the ideal values for x and k until finally it has a minimal answer for y using ideal answers for both x and k. I’m not sure what the actual answer is, so I’m letting it stop within a range of 10. If it works, I’ll make it smaller, but I don’t want the program going for forever, just in case.

MY PROBLEM: I keep getting overflow errors! I’m trying to round the values for xmin and kmin to three figures after the decimal, but it doesn’t seem to be helping. Am I using them wrong? Can someone help me get this program working?

Answer 1

You’re doing a division by zero. xmin = 0, k = 0, (xmin + k) ^ 2 = 0. (I’m not sure why it isn’t reporting division by zero.)

A suggestion: use the Locals pane to see the value of local variables. You can also use the Watch pane to see the value of expressions you want to monitor.