Help with Excel trendlines

[plunar]

Excel's trendline options are rather pathetic.

I do not know why, but in the trendline options excel has the logarithmic curves option greyed out. However, these data are clearly suited for a logarithmic curve. why is excel giving me a hard time? these curves are not polynominals!

 

[clevin]

if its logarithm, it might be better u change the x axis to logarithm, so u get a near straight line.

 

[plunar]

the trendline should look like this:

http://en.wikipedia.org/wiki/Image:Logarithms.png

don't understand why microsoft makes this so damn difficult....

 

[balamw]

the trendline should look like this:

http://en.wikipedia.org/wiki/Image:Logarithms.png

don't understand why microsoft makes this so damn difficult....

What happens if you make your y axis start at something other than zero (and make sure you have no zeros in your data)?

Since the log of zero or a negative number diverge or are undefined, MS greys the option out.

Still, I agree Excel is lousy for XY plots.

B

 

[plunar]

okay so taking out the first row, where x values equal zero, fixed the trendlines. they still are lousy fits though. is there another program (free) i can use for this?

 

[iSaint]

Grapher is on my G4 Powerbook under Applications > Utilities. Check that location...

 

[balamw]

You could also try gnuplot, available for Mac here among other places. http://www.hmug.org/pub/MacOS_X/X/Applications/Math/gnuplot/

B

 

[MisterMe]

Excel's trendline options are rather pathetic.

I do not know why, but in the trendline options excel has the logarithmic curves option greyed out. However, these data are clearly suited for a logarithmic curve. why is excel giving me a hard time? these curves are not polynominals!

Not to belabor the obvious, but as a charting application Excel is very blunt intrument. There are dedicated charting apps which do a beautiful job with Excel data. My personal favorite is KaleidaGraph. Many swear by DeltaGraph which specializes in graphing Excel data. You can find other charting apps here and there.