And lo on Fri, 09 May 2008 22:42:05 +0100, Chambers  
<bdc### [at] yahoocom> did spake, saying:

> So I have a certain function f(x), where x is a positive integer value.
>
> I would like another function g(y) which is the sum of all values of  
> f(x), with x ranging from 0..y
>
> This is trivial using Sigma notation.  Unfortunately, this is not  
> available in
> any spreadsheet I know of (I use MS Office at work, and OpenOffice.org at
> home).

I think the assumption is that anyone who knows Sigma notation will  
already know both the geometric and arithmetic progression formulas.

> I'd rather not write a macro for this,
[snip]

How would you input the x value into the function? if you had your  
M*R*(D^x) then had a GEOPROG(lower, upper, step, formula) how would you  
write the formula containing the variable x in a way Excel (or any  
spreadsheet) could interpret?

> Not to mention that every time I opened the spreadsheet, I'd have to  
> deal with those annoying security warnings about dangerous macros.

Yes annoying, but understandable that user-defined functions trigger the  
macro security flag. Though if it's something you're going to use a lot  
then you could just sign it and add the signature as a trusted source.

> I could populate an entire column on a separate sheet with the values I  
> need,

Yes unfortunately that's what the Excel SERIESSUM formula requires, and it  
wouldn't work for you anyway as the formula equivalent is sum(x*(D^x))  
where x is the range.

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

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