Logarithmic Trendline

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Level 7

30,648 points

Logarithmic Trendline

I am testing out iWork '09, hoping to get away from Office. So, naturally, I'm importing a few of my Office documents (Word docs and Excel spreadsheets so far) to see what happens. I've run into a problem with Numbers and hope someone can help. This problem isn't about an import issue, it seems to be a problem with trendlines in Numbers.

I have created a scatter chart with a logarithmic X axis, linear Y axis, and a logarithmic trendline. A log trendline on this chart should be a straight line. The trendline equation is correct and I can create and plot a second series using the equation but the trendline plotted by Numbers is nowhere near correct. The trendline is plotted as if the X axis is a linear scale, which it is not. In fact, if I change X to a linear scale, the trendline looks exactly the same as before (but is now correct).

Any ideas, am I doing something wrong?

Mac Pro 2008, Mac OS X (10.5.6)

Posted on Feb 9, 2009 6:26 PM

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Answer 1

KOENIG Yvan

Level 8

41,819 points

Feb 10, 2009 7:44 AM in response to Badunit

Which behavior if you swap the values and set the Y axis as logarithmic ?

Yvan KOENIG (from FRANCE mardi 10 février 2009 16:44:03)

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Answer 2

Badunit Author

Level 7

30,648 points

Feb 10, 2009 12:41 PM in response to KOENIG Yvan

I don't know, I'll have to try it out. Even if it works, though, the trendline (the actual equation, not just the plot) with the data flipped will be different from it the other way. The two trendline equations will not be equivalent to each other.

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Answer 3

KOENIG Yvan

Level 8

41,819 points

Feb 10, 2009 1:15 PM in response to Badunit

Send me a sample file with a set of datas.

If it behave flawlessly here, I will post a bug report.

Click my blue name to get my address.

Yvan KOENIG (from FRANCE mardi 10 février 2009 22:15:19)

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Answer 4

Badunit Author

Level 7

30,648 points

Feb 10, 2009 1:37 PM in response to KOENIG Yvan

For the original problem, it is easy to create a simple 5 datapoint logarithmic chart with a trendline by just making up some numbers. I can't send you my data because it is company proprietary. I put in feedback to Apple, I'm sure a bug report will go in soon from someone else with the same problem. I think I'll drop it at this time. I can do without the trendline plots for a while as long as I can get the equations (which seem to be correct).

On the issue of trendlines being non-equivalent when swapping the X and Y axis, that is not a bug so no action is required.

Thanks.

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Answer 5

KOENIG Yvan

Level 8

41,819 points

Feb 11, 2009 10:02 AM in response to Badunit

I apologize, I may send a bug report but I have no time available to build an exemple of the problem which you encounter.

So, no sample file means no report.

Yvan KOENIG (from FRANCE mercredi 11 février 2009 19:02:09)

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Answer 6

Badunit Author

Level 7

30,648 points

Feb 11, 2009 10:32 AM in response to KOENIG Yvan

No problem. Thanks for your help.

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