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Date: Tue, 7 May 2013 15:15:17 +0000 (UTC)
From: "Gilles (JIRA)" <jira@apache.org>
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Message-ID: <JIRA.12646213.1367846705316.281086.1367939717671@arcas>
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Subject: [jira] [Commented] (MATH-972) LinearInterpolator Misconception
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    [ https://issues.apache.org/jira/browse/MATH-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13650950#comment-13650950 ] 

Gilles commented on MATH-972:
-----------------------------

bq. [...] about the object returned by LinearInterpolator [...] should not be derivable on the entire domain [...]

Strictly speaking it is not, since the "interpolate" method in "UnivariateInterpolator" is defined to return a "UnivariateFunction".
The actual object used is an "implementation detail" which users should not rely on.

At first sight, your "PiecewiseLinearFunction" is just another name for a special case of our "PolynomialSplineFunction" (where all its components have degree 1). IMHO, it doesn't warrant the code duplication.

It seemed that the name "PolynomialSplineFunction" is at the origin of the confusion.

                
> LinearInterpolator Misconception
> --------------------------------
>
>                 Key: MATH-972
>                 URL: https://issues.apache.org/jira/browse/MATH-972
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.2
>         Environment: All
>            Reporter: oskar_hertwig
>            Priority: Trivial
>         Attachments: PiecewiseLinearFunction.java, Test.java
>
>   Original Estimate: 2h
>  Remaining Estimate: 2h
>
> The method interpolate() of the class LinearInterpolator return a polynomialSplineFunction althought a piecewiseContinuousFunction have to be returned.
> This cause a bug. Indeed when the interpolated serie is localy constant the linear interpolation should lead to constant value between this points. This is not possible when the returned object is a PolynomialSplineFunction

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