Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Posted to microsoft.public.excel.misc
external usenet poster
 
Posts: 2
Default how to solve equations in excel that involve iterations?

The equation has one unknown, but appear on both sides of the equation:

A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)]

THe only unknown that need to be solved is A. B, C, D, and E are known
variables. How to solve?
  #2   Report Post  
Posted to microsoft.public.excel.misc
external usenet poster
 
Posts: 762
Default how to solve equations in excel that involve iterations?

san2000 -

Maybe you could use Goal Seek (to change A by trying to set the difference
between the left and right sides of your equation to the value zero).

For example, using the values B=2, C=3, D=4, and E=5, I entered the
following in cell B1:

=A1+2/2-SQRT(3/4)*((5-A1)^(3/2))/((A1-2)^(1/2))

Then I entered a tentative value of 3 in cell A1.

Then I chose Tools | Goal Seek, and used Set Cell B1, To Value 0 (zero), and
By Changing Cell A1.

For more precision, choose Tools | Options | Calculation, and enter a
smaller value for Maximum Change. You do not need to check the Iterations
box.

- Mike
http://www.mikemiddleton.com

"san2000" wrote in message
...
The equation has one unknown, but appear on both sides of the equation:

A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)]

THe only unknown that need to be solved is A. B, C, D, and E are known
variables. How to solve?



  #3   Report Post  
Posted to microsoft.public.excel.misc
external usenet poster
 
Posts: 2
Default how to solve equations in excel that involve iterations?

Thanks Mike. I use Goal Seek, but find out that it can only apply one cell
at a time. Is there a way to make the process faster? Will Macro helps in
this situation? I'm not familar with Macro at all. Any help would be great.
Thanks in advance.

"Mike Middleton" wrote:

san2000 -

Maybe you could use Goal Seek (to change A by trying to set the difference
between the left and right sides of your equation to the value zero).

For example, using the values B=2, C=3, D=4, and E=5, I entered the
following in cell B1:

=A1+2/2-SQRT(3/4)*((5-A1)^(3/2))/((A1-2)^(1/2))

Then I entered a tentative value of 3 in cell A1.

Then I chose Tools | Goal Seek, and used Set Cell B1, To Value 0 (zero), and
By Changing Cell A1.

For more precision, choose Tools | Options | Calculation, and enter a
smaller value for Maximum Change. You do not need to check the Iterations
box.

- Mike
http://www.mikemiddleton.com

"san2000" wrote in message
...
The equation has one unknown, but appear on both sides of the equation:

A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)]

THe only unknown that need to be solved is A. B, C, D, and E are known
variables. How to solve?




  #4   Report Post  
Posted to microsoft.public.excel.misc
external usenet poster
 
Posts: 762
Default how to solve equations in excel that involve iterations?

san2000 -

Your description of your problem specifically stated there was only one
unknown, so Goal Seek is appropriate. If you have several unknowns, Excel's
Solver may be more appropriate.

In general, a macro (VBA) will not be faster than Excel's built-in features.

- Mike

"san2000" wrote in message
...
Thanks Mike. I use Goal Seek, but find out that it can only apply one
cell
at a time. Is there a way to make the process faster? Will Macro helps
in
this situation? I'm not familar with Macro at all. Any help would be
great.
Thanks in advance.

"Mike Middleton" wrote:

san2000 -

Maybe you could use Goal Seek (to change A by trying to set the
difference
between the left and right sides of your equation to the value zero).

For example, using the values B=2, C=3, D=4, and E=5, I entered the
following in cell B1:

=A1+2/2-SQRT(3/4)*((5-A1)^(3/2))/((A1-2)^(1/2))

Then I entered a tentative value of 3 in cell A1.

Then I chose Tools | Goal Seek, and used Set Cell B1, To Value 0 (zero),
and
By Changing Cell A1.

For more precision, choose Tools | Options | Calculation, and enter a
smaller value for Maximum Change. You do not need to check the Iterations
box.

- Mike
http://www.mikemiddleton.com

"san2000" wrote in message
...
The equation has one unknown, but appear on both sides of the equation:

A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)]

THe only unknown that need to be solved is A. B, C, D, and E are known
variables. How to solve?






  #5   Report Post  
Posted to microsoft.public.excel.misc
external usenet poster
 
Posts: 947
Default how to solve equations in excel that involve iterations?

Hi. Just some thoughts.
With multiple square roots, it brings to mind multiple solutions. Also,
note that it ae, or a<b, then you will be working with Complex numbers.
(Sqrt of negative numbers). Does this constraint hold? b<a<e? If C is the
opposite sign of D, you will have a sqrt of a negative number as well.
One additional method could be the Newton Equation. Goal Seek works great,
but can be limited in its accuracy. However, you can loop a few more times
in your own function.
This isn't fancy, and it doesn't have much error checking. Here's a simple
example using Mike's numbers...

Sub TestIt()
Debug.Print Fx(2, 3, 4, 5)
End Sub

Function Fx(b, c, d, e)
Dim K1
Dim K2
Dim a
Dim Num
Dim Den
Dim Last

K1 = b / 2
K2 = Sqr(c / d)
Last = 0
a = (b + e) / 2 'Middle
Do While Last < a
Last = a
Num = a + K1 - ((K2 * (e - a) ^ (3 / 2)) / Sqr(a - b))

Den = ((Sqr(e - a) * (2 * a - 3 * b + e) * K2) / _
(a - b) ^ (3 / 2) + 2) / 2

a = a - Num / Den
Debug.Print a

If a e Then a = e
If a < b Then a = b + 0.00001
Loop
End Function

Returns a = 2.68510380165928
which checks...

--
HTH :)
Dana DeLouis
Windows XP & Office 2003


"san2000" wrote in message
...
The equation has one unknown, but appear on both sides of the equation:

A+B/2 = SQRT(C/D) * [(E - A)^(3/2)] / [(A - B)^(1/2)]

THe only unknown that need to be solved is A. B, C, D, and E are known
variables. How to solve?





Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to graph functions and equations in excel How to graph functions and equations Charts and Charting in Excel 2 August 30th 06 01:00 PM
excel doest not shows the number starting with 0..is there is any way to solve this. naughtyboy Excel Discussion (Misc queries) 2 August 9th 06 08:01 PM
Need suggestions for some uses of Ms Excel Bible John Excel Discussion (Misc queries) 1 February 27th 06 05:30 PM
TRYING TO SET UP EXCEL SPREADSHEET ON MY COMPUTER MEGTOM New Users to Excel 5 October 27th 05 03:06 AM
Excel Range Value issue (Excel 97 Vs Excel 2003) Keeno Excel Discussion (Misc queries) 2 June 13th 05 02:01 PM


All times are GMT +1. The time now is 03:46 PM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 ExcelBanter.
The comments are property of their posters.
 

About Us

"It's about Microsoft Excel"