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Bug 75655 - EDITING: Exponential smoothing uses incorrect formula
Summary: EDITING: Exponential smoothing uses incorrect formula
Status: RESOLVED NOTABUG
Alias: None
Product: LibreOffice
Classification: Unclassified
Component: Calc (show other bugs)
Version:
(earliest affected)
4.2.1.1 release
Hardware: x86-64 (AMD64) All
: medium normal
Assignee: Tomaz Vajngerl
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2014-03-02 00:52 UTC by Peter Beurle
Modified: 2015-03-22 01:11 UTC (History)
3 users (show)

See Also:
Crash report or crash signature:


Attachments
Sample showing Excel vs LO results (19.29 KB, application/vnd.oasis.opendocument.spreadsheet)
2014-03-02 00:52 UTC, Peter Beurle
Details

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Description Peter Beurle 2014-03-02 00:52:30 UTC
Created attachment 94945 [details]
Sample showing Excel vs LO results

When using the exponential smoothing option under the new statistics menu it exhibits the following problems;

1. The first result in the series should be #N/A as it has no previous data.

2. The cell references are incorrect on several counts

3. The results are the same as the input

Also, would it be possible to supress the column headers with a option in the dialog box?

When compared to Excel, putting the alpha value into a separate cell is a good idea.
Comment 1 Tomaz Vajngerl 2014-03-02 11:17:45 UTC
Hi,

1. The first "result" is the initial forecast, which can be calculated in many ways and it is usually the first value. See [1] and related links.

2 and 3. Your data is row oriented so you have to set "Group By" to row. The output is always column oriented tough - maybe it should depend on the "Group By" selection. 

Also note that in Excel's "Damping factor" = (1 - Alpha). When you set "Damping factor" to 0.7 this means Alpha is 0.3; Who knows why they did it this way as it is clearly misleading.

Suppressing of column headers is a to-do.

[1]: http://en.wikipedia.org/wiki/Exponential_smoothing
Comment 2 Julien Nabet 2015-03-21 21:56:03 UTC
Tomaz: reading your comment about this one, should we put "NOTABUG"?
Comment 3 Tomaz Vajngerl 2015-03-22 01:11:57 UTC
Yes, I have set it to NOTABUG.