Issue 120419 - strange cubic smoothing algorithm
Summary: strange cubic smoothing algorithm
Status: CLOSED NOT_AN_OOO_ISSUE
Alias: None
Product: General
Classification: Code
Component: chart (show other issues)
Version: 3.3.0 or older (OOo)
Hardware: All All
: P3 Minor (vote)
Target Milestone: ---
Assignee: AOO issues mailing list
QA Contact:
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2012-07-31 13:13 UTC by Balazs.Klein
Modified: 2013-02-24 21:21 UTC (History)
1 user (show)

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Issue Type: DEFECT
Latest Confirmation in: ---
Developer Difficulty: ---

Attachments
cubic smoothed linechart with inflection point at the wrong place (1.98 KB, image/gif)
2012-07-31 13:13 UTC, Balazs.Klein 		no flags Details
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Description Balazs.Klein 2012-07-31 13:13:35 UTC 
Created attachment 78790 [details]
cubic smoothed linechart with inflection point at the wrong place

In a case where the points are 1, 5, 4 the highest point of the smoothed curve should be 5. Currently its higher.

When creating a cubic smoothed linechart the inflection point of the curve currently may fall before or after the actual datapoint. This is a problem because it creates the illusion that there maybe values larger (or smaller) than the largest (or smallest) datapoint.
Comment 1 Regina Henschel 2012-07-31 13:38:18 UTC 
That is no error but the property of cubic splines. Your given points have the coordinate (1|1) (2|5) and (3|4). An interpolating polynom for your given points is y = -2.5 * x^2 + 11.5 * x - 8. And that polynom has its maximum at x=2.25 with a maximum value of 5.125