Equations & Charts.

[ronbar]

Hi everybody,

I rlly nead ur help to solve ma little problem.
I just want to know how to plot an graph or chart using certain equation. For example, i wanna plot this: y=x+3. so how to draw a graph without putting the values and juss writing the equation?

cheers

 

[Carl Witthoft]

Hi everybody,

I rlly nead ur help to solve ma little problem.
I just want to know how to plot an graph or chart using certain equation. For
example, i wanna plot this: y=x+3. so how to draw a graph without putting the
values and juss writing the equation?

cheers

Use Gnuplot (joke).
But, in fact, There are a lot of freeware and shareware tools that will
graph an equation for you, with varying quality and option sets. Surf
macupdate.com to find a bunch. -- or does that Calc tool still come
preloaded w/ MacOS? I forget.

You need to understand that Excel does not "do" equations. The only
thing it does is calculate values in cells, using "formulas." These
look like equations but really aren't. The only way to plot something
is to fill a column with x values and another column with the formula to
produce y values.

 

[Mike Middleton]

ronbar -

With Excel, the usual approach is to enter some x values in a column, enter
a formula for your equation in an adjacent column referring to the x values,
select both columns of data, and create an XY (Scatter) chart. Since your
example is linear, it would require only two XY points.

Stephen Bullen has an example worksheet that allows you to plot a function
without putting values on the worksheet. The download file is named
ChtFrmla.zip, and it's available from
http://www.bmsltd.ie/Excel/Default.htm
or directly from
http://www.bmsltd.ie/DLCount/DLCount.asp?file=ChtFrmla.zip

- Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel

 

[Carl Witthoft]

I'm not an expert, but my weak detective skills tell me that "Evaluate"
is a VBA function, so the referenced workbook is cheating, so to speak.
You can do most anything you want with macro tools.
And given the little oddity with Office 2008, that ChtFrmla file
isn't going to be much good for a while.

 

[Mike Middleton]

Carl Witthoft -

"Evaluate" is an Excel VBA method, but EVALUATE is also an Excel 4 XLM macro
function.

Generally, Excel 4 XLM macro functions can be used as "refers to" for
defined names, which is the approach Stephen Bullen used in ChtFrmla.xls.

And all versions of Excel since Excel 4, Windows and Mac, support Excel 4
XLM code.

The original poster did not specify which version of Excel he is using.

My limited testing indicates that Stephen Bullen's ChtFrmla.xls (which was
saved as an Excel 5.0/95 workbook) works fine in Windows Excel 97 and 2008
and in Mac Excel 2004. So far I haven't gotten it to work in Windows Excel
2003 or in Mac Excel 2008.

- Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel

 

[Carl Witthoft]

Interesting. Thanks for the pointer. Given the results of your
testing, it appears Bullen used VBA to build his function. I suppose
one could rewrite it using XLM macro .

 

[Mike Middleton]

Carl Witthoft -

There is no VBA code in Stephen Bullen's ChtFrmla.xls workbook.

The only slightly-nonstandard portion is the Excel 4 XLM macro function
EVALUATE in the defined name y.

I don't know why I can't get it to work on Windows Excel 2003 and Mac Excel
2008.

- Mike Middleton