I have a equation that you can solve only by trial an error, but I wan
excel to do the work for me. The equation is this

1/(X^.5)=2Log(C*X^.5)-.8
Where c is some constant that isant worth mentioning ;)
and the Log is base 10.
Ok I need a macro that will keep trying values untill one side is equa
to the other up to .001 decimal places. I tried making some sort o
random function generator, but it seems like the random function kep
repeating certain values. Any advice/help is appericated.
-Mar

--
Message posted from http://www.ExcelForum.com

I came up with 3.73250246, ignoring C

"medialint" wrote:

Something like this, though if C isn't worth mentioning then why put it in?

Sub LoopSolve()
Randomize
Dim myRandomNum As Single
Dim YRow As Long
Dim XAdd As Long
Dim CalcDiff As Single
YRow = 2
Worksheets("Sheet1").Cells(1, 1) = "Number"
Worksheets("Sheet1").Cells(1, 2) = "Difference"
Do
myRandomNum = Rnd * 1000
CalcDiff = Abs((1 / (myRandomNum ^ 0.5)) - (2 * Log(myRandomNum ^ 0.5) - 0.8))
Worksheets("Sheet1").Cells(YRow, 1 + XAdd) = myRandomNum
Worksheets("Sheet1").Cells(YRow, 2 + XAdd) = CalcDiff
YRow = YRow + 1
If YRow 65536 Then
YRow = 2
XAdd = XAdd + 2
End If
Loop Until CalcDiff < 0.001
End Sub


"mrmark " wrote:

I have a equation that you can solve only by trial an error, but I want
excel to do the work for me. The equation is this

1/(X^.5)=2Log(C*X^.5)-.8
Where c is some constant that isant worth mentioning ;)
and the Log is base 10.
Ok I need a macro that will keep trying values untill one side is equal
to the other up to .001 decimal places. I tried making some sort of
random function generator, but it seems like the random function kept
repeating certain values. Any advice/help is appericated.
-Mark


---
Message posted from http://www.ExcelForum.com/

Sorry, but the formula needs a slight tweak. The log
functtion in VBA is a natural log function not Log10.
Also the formula will give negative answers so will meet
the <.0001 criteria. Change the routine as follows:

CalcDiff = Abs((1 / (myRandomNum ^ 0.5)) - (2 * (Log
(myRandomNum ^ 0.5)/log(10#)) - 0.8))

and

Loop Until CalcDiff < 0.001 and Calcdiff -.001

All the best

DavidC

-----Original Message-----
I came up with 3.73250246, ignoring C

"medialint" wrote:

Something like this, though if C isn't worth mentioning
then why put it in?

Sub LoopSolve()
Randomize
Dim myRandomNum As Single
Dim YRow As Long
Dim XAdd As Long
Dim CalcDiff As Single
YRow = 2
Worksheets("Sheet1").Cells(1, 1) = "Number"
Worksheets("Sheet1").Cells(1, 2) = "Difference"
Do
myRandomNum = Rnd * 1000
CalcDiff = Abs((1 / (myRandomNum ^ 0.5)) - (2 *
Log(myRandomNum ^ 0.5) - 0.8))
Worksheets("Sheet1").Cells(YRow, 1 + XAdd) =
myRandomNum
Worksheets("Sheet1").Cells(YRow, 2 + XAdd) =
CalcDiff
YRow = YRow + 1
If YRow 65536 Then
YRow = 2
XAdd = XAdd + 2
End If
Loop Until CalcDiff < 0.001
End Sub


"mrmark " wrote:

I have a equation that you can solve only by trial an
error, but I want
excel to do the work for me. The equation is this

1/(X^.5)=2Log(C*X^.5)-.8
Where c is some constant that isant worth
mentioning ;)
and the Log is base 10.
Ok I need a macro that will keep trying values untill
one side is equal
to the other up to .001 decimal places. I tried
making some sort of
random function generator, but it seems like the
random function kept
repeating certain values. Any advice/help is
appericated.
-Mark


---
Message posted from http://www.ExcelForum.com/


.

Forgot to remind you to add in the constant. So try the
routine from medialint as revised below to fix the natural
log problem and the negative value issue and add in the
constant. I have referenced cell C1 for the constant to
make it easier for the constant to be changed without
going to the routine. Also if you want, add Msgbox
(myrandomnum) after the Loop statement to give you the
answer quickly without having to search for it.


Sub LoopSolve()
Randomize
Dim myRandomNum As Single
Dim YRow As Long
Dim XAdd As Long
Dim CalcDiff As Single
YRow = 2
Worksheets("Sheet1").Cells(1, 1) = "Number"
Worksheets("Sheet1").Cells(1, 2) = "Difference"
con = ActiveSheet.Range("C1").Value

Do
myRandomNum = Rnd * 100
CalcDiff = Abs(1 / (myRandomNum ^ 0.5)) - (2 *
con * (Log(myRandomNum ^ 0.5) / Log(10#)) - 0.8)
Worksheets("Sheet1").Cells(YRow, 1 + XAdd) =
myRandomNum
Worksheets("Sheet1").Cells(YRow, 2 + XAdd) =
CalcDiff
YRow = YRow + 1
If YRow 65536 Then
YRow = 2
XAdd = XAdd + 2
End If
Loop Until CalcDiff < 0.001 And CalcDiff -0.001

End Sub

Best of luck

DavidC
-----Original Message-----
I have a equation that you can solve only by trial an
error, but I want
excel to do the work for me. The equation is this

1/(X^.5)=2Log(C*X^.5)-.8
Where c is some constant that isant worth mentioning ;)
and the Log is base 10.
Ok I need a macro that will keep trying values untill one
side is equal
to the other up to .001 decimal places. I tried making
some sort of
random function generator, but it seems like the random
function kept
repeating certain values. Any advice/help is appericated.
-Mark


---
Message posted from http://www.ExcelForum.com/

.